Methods and apparatus to form biocompatible energization primary elements for biomedical devices

ABSTRACT

Methods and apparatus to form biocompatible energization elements are described. In some embodiments, the methods and apparatus to form the biocompatible energization elements involve forming cavities comprising active cathode chemistry. The active elements of the cathode and anode are sealed with a laminate stack of biocompatible material. In some embodiments, a field of use for the methods and apparatus may include any biocompatible device or product that requires energization elements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/040,178 filed Aug. 21, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods and apparatus to form biocompatible energization elements aredescribed herein. In some embodiments, the methods and apparatus to formthe biocompatible energization elements involve forming a separatorelement in the energization element. The active elements includinganodes, cathodes and electrolytes may be electrochemically connected andmay interact with the formed separator elements. In some embodiments, afield of use for the methods and apparatus may include any biocompatibledevice or product that requires energization elements.

2. Discussion of the Related Art

Recently, the number of medical devices and their functionality hasbegun to rapidly develop. These medical devices can include, forexample, implantable pacemakers, electronic pills for monitoring and/ortesting a biological function, surgical devices with active components,contact lenses, infusion pumps, and neurostimulators. Addedfunctionality and an increase in performance to many of theaforementioned medical devices has been theorized and developed.However, to achieve the theorized added functionality, many of thesedevices now require self-contained energization means that arecompatible with the size and shape requirements of these devices, aswell as the energy requirements of the new energized components.

Some medical devices may include components such as semiconductordevices that perform a variety of functions and can be incorporated intomany biocompatible and/or implantable devices. However, suchsemiconductor components require energy and, thus, energization elementsshould preferably also be included in such biocompatible devices. Thetopology and relatively small size of the biocompatible devices createsnovel and challenging environments for the definition of variousfunctionalities. In many embodiments, it is important to provide safe,reliable, compact and cost effective means to energize the semiconductorcomponents within the biocompatible devices. Therefore, a need existsfor novel embodiments of forming biocompatible energization elements forimplantation within or upon biocompatible devices where the structure ofthe battery elements provides enhanced containment for chemicalcomponents of the energization elements as well as improved control overthe quantity of chemical components contained in the energizationelement.

SUMMARY OF THE INVENTION

Accordingly, methods and apparatus to form biocompatible energizationelements are disclosed which afford manufacturing advantages whilecreating structures which may significantly contain the batterychemistry. As well, the structural design may also provide for inherentcontrol of the quantities of the energization elements found within thebattery elements.

One general aspect includes a biocompatible energization elementincluding a gap spacer layer; a first hole located in the gap spacerlayer; a cathode spacer layer, where the cathode spacer layer isattached to the gap spacer layer; a second hole located in the cathodespacer layer, where the second hole is aligned to the first hole, andwhere the second hole is smaller than the first hole such that when thefirst hole and the second hole are aligned there is a ridge of cathodespacer layer exposed in the first hole. The biocompatible energizationelement also includes a separator layer, where the separator layer isplaced within the first hole in the gap spacer layer and is adhered tothe ridge of cathode spacer layer. The biocompatible energizationelement also includes a cavity between sides of the second hole and afirst surface of the separator layer, where the cavity is filled withcathode chemicals. The biocompatible energization element also includesa first current collector coated with anode chemicals. The biocompatibleenergization element also includes a second current collector, where thesecond current collector is in electrical connection with the cathodechemicals. The biocompatible energization element also includes anelectrolyte including electrolyte chemicals. The biocompatibleenergization element also includes the cathode chemicals, anodechemicals and electrolyte chemicals being formulated for a singledischarging cycle of the energization element.

Implementations may include one or more of the following features: thebiocompatible energization element where the cathode chemicals include asalt of manganese including manganese dioxide; the biocompatibleenergization element where the anode chemicals include zinc includingelectrodeposited zinc; the biocompatible energization element where thecathode chemicals include graphite, polyisobutylene, toluene, jet milledelectrolytic manganese dioxide, and KS6 primary synthetic graphite; thebiocompatible energization element where the cathode chemicals include amixture approximately of 1.5 parts 10 percent PIB B50 in toluene to 2.3parts additional toluene to 4.9 parts of a mixture includingapproximately 80 percent jet milled electrolytic manganese dioxide to 20percent KS6 primary synthetic graphite; the biocompatible energizationelement where the electrolyte includes zinc chloride and ammoniumchloride; and the biocompatible energization element where the separatorincludes Celgard 412.

The biocompatible energization element where the biocompatibleenergization element is electrically connected to an electroactiveelement within a biomedical device such as an ophthalmic device such asa contact lens. The biocompatible energization element where thebiocompatible energization element is electrically connected to anelectroactive element within a biomedical device. The biocompatibleenergization element where the separator includeshydroxyethylmethacrylate, ethylene glycol dimethylacrylate andpolyvinylpyrrolidone.

The biocompatible energization element where the cathode chemicalsinclude a mixture approximately of 1.5 parts 10 percent PIB B50 intoluene to 2.3 parts additional toluene to 4.9 parts of a mixtureincluding approximately 80 percent jet milled electrolytic manganesedioxide to 20 percent KS6 primary synthetic graphite, where the anodechemicals include electrodeposited zinc, and where the electrolyteincludes zinc chloride and ammonium chloride; the biocompatibleenergization element where the biocompatible energization element iselectrically connected to an electroactive element within a biomedicaldevice; the biocompatible energization element where the biomedicaldevice is an ophthalmic device; the biocompatible energization elementwhere the ophthalmic device is a contact lens.

One general aspect includes a biocompatible energization elementincluding a cathode spacer layer. The biocompatible energization elementalso includes a first hole located in the cathode spacer layer. Thebiocompatible energization element also includes a first currentcollector coated with anode chemicals, where the first current collectoris attached to a first surface of the cathode spacer layer, and where afirst cavity is created between sides of the first hole and a firstsurface of the first current collector coated with anode chemicals. Thebiocompatible energization element also includes a separator layer,where the separator layer is formed within the first cavity after aseparator precursor mixture is dispensed into the cavity. Thebiocompatible energization element also includes a second cavity betweensides of the first hole and a first surface of the separator layer,where the second cavity is filled with cathode chemicals. Thebiocompatible energization element also includes a second currentcollector, where the second current collector is in electricalconnection with the cathode chemicals. The biocompatible energizationelement also includes an electrolyte including electrolyte chemicals.The biocompatible energization element also includes where the cathodechemicals, anode chemicals and electrolyte chemicals are formulated fora single discharging cycle of the energization element.

Implementations may include one or more of the following features. Thebiocompatible energization element where the separator includeshydroxyethylmethacrylate, ethylene glycol dimethylacrylate andpolyvinylpyrrolidone. The biocompatible energization element where thecathode chemicals include a mixture approximately of 1.5 parts 10percent PIB B50 in toluene to 2.3 parts additional toluene to 4.9 partsof a mixture including approximately 80 percent jet milled electrolyticmanganese dioxide to 20 percent KS6 primary synthetic graphite, wherethe anode chemicals include electrodeposited zinc, and where theelectrolyte includes zinc chloride and ammonium chloride.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1D illustrate exemplary aspects of biocompatible energizationelements in concert with the exemplary application of contact lenses.

FIG. 2 illustrates the exemplary size and shape of individual cells ofan exemplary battery design.

FIG. 3A illustrates a first stand-alone, packaged biocompatibleenergization element with exemplary anode and cathode connections.

FIG. 3B illustrates a second stand-alone, packaged biocompatibleenergization element with exemplary anode and cathode connections.

FIGS. 4A-4N illustrate exemplary method steps for the formation ofbiocompatible energization elements for biomedical devices.

FIG. 5 illustrates an exemplary fully formed biocompatible energizationelement.

FIGS. 6A-6F illustrate exemplary method steps for structural formationof biocompatible energization elements.

FIGS. 7A-7F illustrate exemplary method steps for structural formationof biocompatible energization elements with alternate electroplatingmethod.

FIGS. 8A-8H illustrate exemplary method steps for the formation ofbiocompatible energization elements with hydrogel separator forbiomedical devices.

FIGS. 9A-C illustrate exemplary methods steps for structural formationof biocompatible energization elements utilizing an alternativeseparator processing embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Methods and apparatus to form three-dimensional biocompatibleenergization elements are disclosed in this application. The separatorelement within the energization elements may be formed with novelmethods and may comprise novel materials. In the following sections,detailed descriptions of various embodiments are described. Thedescription of both preferred and alternative embodiments are exemplaryembodiments only, and various modifications and alterations may beapparent to those skilled in the art. Therefore, the exemplaryembodiments do not limit the scope of this application. Thethree-dimensional biocompatible energization elements are designed foruse in or proximate to the body of a living organism.

Glossary

In the description and claims below, various terms may be used for whichthe following definitions will apply:

“Anode” as used herein refers to an electrode through which electriccurrent flows into a polarized electrical device. The direction ofelectric current is typically opposite to the direction of electronflow. In other words, the electrons flow from the anode into, forexample, an electrical circuit.

“Binders” as used herein refer to a polymer that is capable ofexhibiting elastic responses to mechanical deformations and that ischemically compatible with other energization element components. Forexample, binders may include electroactive materials, electrolytes,polymers, etc.

“Biocompatible” as used herein refers to a material or device thatperforms with an appropriate host response in a specific application.For example, a biocompatible device does not have toxic or injuriouseffects on biological systems.

“Cathode” as used herein refers to an electrode through which electriccurrent flows out of a polarized electrical device. The direction ofelectric current is typically opposite to the direction of electronflow. Therefore, the electrons flow into the cathode of the polarizedelectrical device and out of, for example, the connected electricalcircuit.

“Coating” as used herein refers to a deposit of material in thin forms.In some uses, the term will refer to a thin deposit that substantiallycovers the surface of a substrate it is formed upon. In other morespecialized uses, the term may be used to describe small thin depositsin smaller regions of the surface.

“Electrode” as used herein can refer to an active mass in the energysource. For example, it may include one or both of the anode andcathode.

“Energized” as used herein refers to the state of being able to supplyelectrical current or to have electrical energy stored within.

“Energy” as used herein refers to the capacity of a physical system todo work. Many uses of the energization elements may relate to thecapacity of being able to perform electrical actions.

“Energy Source” or “Energization Element” or “Energization Device” asused herein refers to any device or layer which is capable of supplyingenergy or placing a logical or electrical device in an energized state.The energization elements may include batteries. The batteries can beformed from alkaline type cell chemistry and may be solid-statebatteries or wet cell batteries.

“Fillers” as used herein refer to one or more energization elementseparators that do not react with either acid or alkaline electrolytes.Generally, fillers may include substantially water insoluble materialssuch as carbon black; coal dust; graphite; metal oxides and hydroxidessuch as those of silicon, aluminum, calcium, magnesium, barium,titanium, iron, zinc, and tin; metal carbonates such as those of calciumand magnesium; minerals such as mica, montmorollonite, kaolinite,attapulgite, and talc; synthetic and natural zeolites such as Portlandcement; precipitated metal silicates such as calcium silicate; hollow orsolid polymer or glass microspheres, flakes and fibers; etc.

“Film” as used herein refers to a thin layer of a material that may actas a covering or a coating; in laminate structures the film typicallyapproximates a planar layer with a top surface and a bottom surface anda body; wherein the body is typically much thinner than the extent ofthe layer.

“Functionalized” as used herein refers to making a layer or device ableto perform a function including, for example, energization, activation,and/or control.

“Mold” as used herein refers to a rigid or semi-rigid object that may beused to form three-dimensional objects from uncured formulations. Somepreferred molds include two mold parts that, when opposed to oneanother, define the structure of a three-dimensional object.

“Power” as used herein refers to work done or energy transferred perunit of time.

“Rechargeable” or “Re-energizable” as used herein refer to a capabilityof being restored to a state with higher capacity to do work. Many usesmay relate to the capability of being restored with the ability to flowelectrical current at a certain rate for certain, reestablished timeperiods.

“Reenergize” or “Recharge” as used herein refer to restoring to a statewith higher capacity to do work. Many uses may relate to restoring adevice to the capability to flow electrical current at a certain ratefor a certain, reestablished time period.

“Released” as used herein and sometimes referred to as “released from amold” means that a three-dimensional object is either completelyseparated from the mold, or is only loosely attached to the mold, sothat it may be removed with mild agitation.

“Stacked” as used herein means to place at least two component layers inproximity to each other such that at least a portion of one surface ofone of the layers contacts a first surface of a second layer. In someembodiments, a coating, whether for adhesion or other functions, mayreside between the two layers that are in contact with each otherthrough said coating.

“Traces” as used herein refer to energization element components capableof connecting together the circuit components. For example, circuittraces can include copper or gold when the substrate is a printedcircuit board and can typically be copper, gold or printed film in aflexible circuit. A special type of “Trace” is the current collector.Current collectors are traces with electrochemical compatibility thatmakes the current collector suitable for use in conducting electrons toand from an anode or cathode in the presence of electrolyte.

The methods and apparatus presented herein relate to formingbiocompatible energization elements for inclusion within or on flat orthree-dimensional biocompatible devices. A particular class ofenergization elements may be batteries that are fabricated in layers.The layers may also be classified as laminate layers. A battery formedin this manner may be classified as a laminar battery.

There may be other examples of how to assemble and configure batteriesaccording to the present disclosure, and some may be described infollowing sections. However, for many of these examples, there areselected parameters and characteristics of the batteries that may bedescribed in their own right. In the following sections, somecharacteristics and parameters will be focused upon.

Exemplary Biomedical Device Construction with Biocompatible EnergizationElements

An example of a biomedical device that may incorporate the EnergizationElements, batteries, of the present disclosure may be an electroactivefocal-adjusting contact lens. Referring to FIG. 1A, an example of such acontact lens insert may be depicted as contact lens insert 100. In thecontact lens insert 100, there may be an electroactive element 120 thatmay accommodate focal characteristic changes in response to controllingvoltages. A circuit 105 to provide those controlling voltage signals aswell as to provide other function such as controlling sensing of theenvironment for external control signals may be powered by abiocompatible battery element 110. As depicted in FIG. 1A, the batteryelement 110 may be found as multiple major pieces, in this case threepieces, and may comprise the various configurations of battery chemistryelements as has been discussed. The battery elements 110 may havevarious interconnect features to join together pieces as may be depictedunderlying the region of interconnect 114. The battery elements 110 maybe connected to a circuit element that may have its own substrate 111upon which interconnect features 125 may be located. The circuit 105,which may be in the form of an integrated circuit, may be electricallyand physically connected to the substrate 111 and its interconnectfeatures 125.

Referring to FIG. 1B, a cross sectional relief of a contact lens 150 maycomprise contact lens insert 100 and its discussed constituents. Thecontact lens insert 100 may be encapsulated into a skirt of contact lenshydrogel 155 which may encapsulate the insert 100 and provide acomfortable interface of the contact lens 150 to a user's eye.

In reference to concepts of the present disclosure, the battery elementsmay be formed in a two-dimensional form as depicted in another exampleof FIG. 1C. In this depiction there may be two main regions of batterycells in the regions of battery component 165 and the second batterycomponent in the region of battery chemistry element 160. The flatelement may connect to a circuit element 163, which in the example ofFIG. 1C may contain two major circuit areas 167. The circuit element 163may connect to the battery element at an electrical contact 161 and aphysical contact 162. The flat structure may be bent into athree-dimensional conical structure as has been described in the presentdisclosure. In that process, a second electrical contact 166 and asecond physical contact 164 may be used to connect and physicallystabilize the three-dimensional structure. Referring to FIG. 1D, arepresentation of this three-dimensional conical structure 180 may befound. The physical and electrical contact points 181 may also be foundand the illustration may be viewed as a three-dimensional view of theresulting structure. This structure may comprise the modular electricaland battery component that will be incorporated with a lens insert intoa biocompatible device.

Segmented Battery Schemes

Referring to FIG. 2, an example of different types of segmented batteryschemes is depicted for an exemplary battery element for a contact lenstype example. The segmented components may be relatively circular-shaped271, square-shaped 272 or rectangular-shaped. In rectangular-shapedexamples, the rectangles can be small rectangular shapes 273, largerrectangular shapes 274, or large rectangular shapes 275.

Custom Shapes of Flat Battery Elements

In some examples of biocompatible batteries, the batteries may be formedas flat elements. Referring to FIG. 3A an example of a rectangularoutline 310 of the battery element may be depicted with an anodeconnection 311 and a cathode connection 312. Referring to FIG. 3B anexample of a circular outline 330 of a battery element may be depictedwith an anode connection 331 and a cathode connection 332.

In some examples of flat-formed batteries, the outlines of the batteryform may be dimensionally and geometrically configured to fit in customproducts. In addition to examples with rectangular or circular outlines,custom “free-form” or “free shape” outlines may be formed which mayallow the battery configuration to be optimized to fit within a givenproduct.

In the exemplary biomedical device case of a variable optic, a“free-form” example of a flat outline may be arcuate in form. The freeform may be of such geometry that when formed to a 3-dimmensional shape,it may take the form of a conical, annular skirt that fits within theconstraining confines of a contact lens. It may be clear that similarbeneficial geometries may be formed where medical devices haverestrictive 2D or 3D shape requirements.

Biocompatibility Aspects of Batteries

As an example, the batteries according to the present disclosure mayhave important aspects relating to safety and biocompatibility. In someexamples, batteries for biomedical devices must meet requirements aboveand beyond those for typical usage scenarios. In some examples, designaspects may be considered related to stressing events. For example, thesafety of an electronic contact lens may need to be considered in theevent a user breaks the lens during insertion or removal. In anotherexample, design aspects may consider the potential for a user to bestruck in the eye by a foreign object. Still further examples ofstressful conditions that may be considered in developing designparameters and constraints may relate to the potential for a user towear the lens in challenging environments like the environment underwater or the environment at high altitude as non-limiting examples.

The safety of such a device may be influenced by the materials that thedevice is formed with, by the quantities of those materials employed inmanufacturing the device, and also by the packaging applied to separatethe devices from the surrounding on- or in-body environment. In anexample, pacemakers may be a typical type of biomedical device which mayinclude a battery and which may be implanted in a user for an extendedperiod of time. Accordingly, in some examples, such pacemakers maytypically be packaged with welded, hermetic titanium enclosures, or inother examples, multiple layers of encapsulation. Emerging poweredbiomedical devices may present new challenges for packaging, especiallybattery packaging. These new devices may be much smaller than existingbiomedical devices, for example, an electronic contact lens or pillcamera may be significantly smaller than a pacemaker. In such examples,the volume and area available for packaging may be greatly reduced.

Electrical Requirements of Microbatteries

Another area for design considerations may relate to electricalrequirements of the device, which must be provided by the battery. Inorder to function as a power source for a medical device, an appropriatebattery may need to meet the full electrical requirements of the systemwhen operating in a non-connected or non-externally powered mode. Anemerging field of non-connected or non-externally powered biomedicaldevices may include, for example, vision-correcting contact lenses,health monitoring devices, pill cameras, and novelty devices. Recentdevelopments in integrated circuit (IC) technology may permit meaningfulelectrical operation at very low current levels, for example, picoampsof standby current and microamps of operating current. IC's may alsopermit very small devices.

Microbatteries for biomedical applications may be required to meet manysimultaneous, challenging requirements. For example, the microbatterymay be required to have the capability to deliver a suitable operatingvoltage to an incorporated electrical circuit. This operating voltagemay be influenced by several factors including the IC process “node,”the output voltage from the circuit to another device, and a particularcurrent consumption target which may also relate to a desired devicelifetime.

With respect to the IC process, nodes may typically be differentiated bythe minimum feature size of a transistor, such as its “so-called”transistor channel. This physical feature, along with other parametersof the IC fabrication, such as gate oxide thickness, can be associatedwith a resulting rating standard for turn-on, or threshold, voltages offield-effect transistors (FET's) fabricated in the given process node.For example, in a node with a minimum feature size of 0.5 microns it maybe common to find FET's with turn-on voltages of 5.0V. However, at aminimum feature size of 90 nm the FET's may turn-on at 1.2, 1.8, and2.5V. The IC foundry may supply standard cells of digital blocks, forexample, inverters and flip-flops that have been characterized and arerated for use over certain voltage ranges. Designers chose an IC processnode based on several factors including density of digital devices,analog/digital mixed signal devices, leakage current, wiring layers, andavailability of specialty devices such as high-voltage FET's. Giventhese parametric aspects of the electrical components which may drawpower from a microbattery, it may be important for the microbatterypower source to be matched to the requirements of the chosen processnode and IC design especially in terms of available voltage and current.

In some examples, an electrical circuit powered by a microbattery, mayconnect to another device. In non-limiting examples, themicrobattery-powered electrical circuit may connect to an actuator or atransducer. Depending on the application, these may include alight-emitting diode (LED), a sensor, a microelectromechanical system(MEMS) pump, or numerous other such devices. In some examples, suchconnected devices may require higher operating voltage conditions thancommon IC process nodes, for example, a variable-focus lens may require35V to activate. The operating voltage provided by the battery maytherefore be a critical consideration when designing such a system. Insome examples of this type of consideration, the efficiency of a lensdriver to produce 35V from a 1V battery may be significantly less thanit might be when operating from a 2V battery. Further requirements suchas die size may be dramatically different considering the operatingparameters of the microbattery as well.

Individual battery cells may typically be rated with open-circuit,loaded, and cutoff voltages. The open-circuit voltage is the potentialproduced by the battery cell with infinite load resistance. The loadedvoltage is the potential produced by the cell with an appropriate, andtypically also specified, load impedance placed across the cellterminals. The cutoff voltage is typically a voltage at which most ofthe battery has been discharged. The cutoff voltage may represent avoltage, or degree of discharge, below which the battery should not bedischarged to avoid deleterious effects, such as excessive gassing. Thecutoff voltage may typically be influenced by the circuit to which thebattery is connected, not just the battery itself, for example, theminimum operating voltage of the electronic circuit. In one example, analkaline cell may have an open-circuit voltage of 1.6V, a loaded voltagein the range 1.0 to 1.5V, and a cutoff voltage of 1.0V. The voltage of agiven microbattery cell design may depend upon other factors of the cellchemistry employed. And, different cell chemistry may therefore havedifferent cell voltages.

Cells may be connected in series to increase voltage; however, thiscombination may come with tradeoffs to size, internal resistance, andbattery complexity. Cells may also be combined in parallelconfigurations to decrease resistance and increase capacity, howeversuch a combination may tradeoff size and shelf life.

Battery capacity may be the ability of a battery to deliver current, ordo work, for a period of time. Battery capacity may typically bespecified in units such as microamp-hours. A battery which can deliver 1microamp of current for 1 hour has 1 microamp-hour of capacity. Capacitymay typically be increased by increasing the mass (and hence volume) ofreactants within a battery device; however, it may be appreciated thatbiomedical devices may be significantly constrained on available volume.Battery capacity may also be influenced by electrode and electrolytematerial.

Depending on the requirements of the circuitry to which the battery isconnected, a battery may be required to source current over a range ofvalues. During storage prior to active use, a leakage current on theorder of picoamps to nanoamps may flow through circuits, interconnects,and insulators. During active operation, circuitry may consume quiescentcurrent to sample sensors, run timers, and perform such low powerconsumption functions. Quiescent current consumption may be on the orderof nanoamps to milliamps. Circuitry may also have even higher peakcurrent demands, for example, when writing flash memory or communicatingover radio frequency (RF). This peak current may extend to tens ofmilliamps or more. The resistance and impedance of a microbattery devicemay also be important to design considerations.

Shelf life typically refers to the period of time which a battery maysurvive in storage and still maintain useful operating parameters. Shelflife may be particularly important for biomedical devices for severalreasons. Electronic devices may displace non-powered devices, as forexample, may be the case for the introduction of an electronic contactlens. Products in these existing market spaces may have establishedshelf life requirements, for example, three years, due to customer,supply chain, and other requirements. It may typically be desired thatsuch specifications not be altered for new products. Shelf liferequirements may also be set by the distribution, inventory, and usemethods of a device comprising a microbattery. Accordingly,microbatteries for biomedical devices may have specific shelf liferequirements, which may be measured in the number of years for example.

In some exemplary embodiments, three-dimensional biocompatibleenergization elements may be rechargeable. For example, an inductivecoil may also be fabricated on the three-dimensional surface. Theinductive coil could then be energized with a radio-frequency (“RF”)fob. The inductive coil may be connected to the three-dimensionalbiocompatible energization element to recharge the energization elementwhen RF is applied to the inductive coil. In another example,photovoltaics may also be fabricated on the three-dimensional surfaceand connected to the three-dimensional biocompatible energizationelement. When exposed to light or photons, the photovoltaics willproduce electrons to recharge the energization element.

In some examples, a battery may function to provide the electricalenergy for an electrical system. In these examples, the battery may beelectrically connected to the circuit of the electrical system. Theconnections between a circuit and a battery may be classified asinterconnects. These interconnects may become increasingly challengingfor biomedical microbatteries due to several factors. In some examples,powered biomedical devices may be very small thus allowing little areaand volume for the interconnects. The restrictions of size and area mayimpact the electrical resistance and reliability of theinterconnections.

In other respects, a battery may contain a liquid electrolyte whichcould boil at high temperature. This restriction may directly competewith the desire to use a solder interconnect which may, for example,require relatively high temperatures such as 250 degrees C. to melt.Although in some examples the battery chemistry, including theelectrolyte, and the heat source used to form solder based interconnectsmay be isolated spatially from each other, in the cases of emergingbiomedical devices, the small size may preclude the separation ofelectrolyte and solder joints by sufficient distance to reduce heatconduction.

Interconnects

Interconnects may allow current to flow to and from the battery inconnection with an external circuit. Such interconnects may interfacewith the environments inside and outside the battery, and may cross theboundary or seal between those environments. These interconnects may beconsidered as traces, making connections to an external circuit, passingthrough the battery seal, and then connecting to the current collectorsinside the battery. As such, these interconnects may have severalrequirements. Outside the battery, the interconnects may resembletypical printed circuit traces. They may be soldered to or otherwiseconnect to other traces. In an example where the battery is a separatephysical element from a circuit board containing an integrated circuit,the battery interconnect may allow for connection to the externalcircuit. This connection may be formed with solder, conductive tape,conductive ink or epoxy, or other means. The interconnect traces mayneed to survive in the environment outside the battery, for example, notcorroding in the presence of oxygen.

As the interconnect passes through the battery seal, it may be ofcritical importance that the interconnect coexist with the seal andpermit sealing. Adhesion may be required between the seal andinterconnect in addition to the adhesion which may be required betweenthe seal and battery package. Seal integrity may need to be maintainedin the presence of electrolyte and other materials inside the battery.Interconnects, which may typically be metallic, may be known as pointsof failure in battery packaging. The electrical potential and/or flow ofcurrent may increase the tendency for electrolyte to “creep” along theinterconnect. Accordingly, an interconnect may need to be engineered tomaintain seal integrity.

Inside the battery, the interconnects may interface with the currentcollectors or may actually form the current collectors. In this regard,the interconnect may need to meet the requirements of the currentcollectors as described herein, or may need to form an electricalconnection to such current collectors.

One class of candidate interconnects and current collectors is metalfoils. Such foils are available in thickness of 25 microns or less,which make them suitable for very thin batteries. Such foil may also besourced with low surface roughness and contamination, two factors whichmay be critical for battery performance. The foils may include zinc,nickel, brass, copper, titanium, other metals, and various alloys.

Electrolyte

An electrolyte is a component of a battery which facilitates a chemicalreaction to take place between the chemical materials of the electrodes.Typical electrolytes may be electrochemically active to the electrodes,for example, allowing oxidation and reduction reactions to occur. Insome examples, this important electrochemical activity may make for achallenge to creating devices that are biocompatible. For example,potassium hydroxide (KOH) may be a commonly used electrolyte in alkalinecells. At high concentration the material has a high pH and may interactunfavorably with various living tissues. On the other hand, in someexamples electrolytes may be employed which may be lesselectrochemically active; however, these materials may typically resultin reduced electrical performance, such as reduced cell voltage andincreased cell resistance. Accordingly, one key aspect of the design andengineering of a biomedical microbattery may be the electrolyte. It maybe desirable for the electrolyte to be sufficiently active to meetelectrical requirements while also being relatively safe for use in- oron-body.

Various test scenarios may be used to determine the safety of batterycomponents, in particular electrolytes, to living cells. These results,in conjunction with tests of the battery packaging, may allowengineering design of a battery system that may meet requirements. Forexample, when developing a powered contact lens, battery electrolytesmay be tested on a human corneal cell model. These tests may includeexperiments on electrolyte concentration, exposure time, and additives.The results of such tests may indicate cell metabolism and otherphysiological aspects. Tests may also include in-vivo testing on animalsand humans.

Electrolytes for use in the present invention may include zinc chloride,zinc acetate, ammonium acetate, and ammonium chloride in massconcentrations from approximately 0.1 percent to 25 percent. Thespecific concentrations may depend on electrochemical activity, batteryperformance, shelf life, seal integrity, and biocompatibility.

In some examples, several classes of additives may be utilized in thecomposition of a battery system. Additives may be mixed into theelectrolyte base to alter its characteristics. For example, gellingagents such as agar may reduce the ability of the electrolyte to leakout of packing, thereby increasing safety. Corrosion inhibitors may beadded to the electrolyte, for example, to improve shelf life by reducingthe undesired dissolution of the zinc anode into the electrolyte.Corrosion inhibitors may include Triton® QS-44 and indium acetate asnon-limiting examples. These inhibitors may positively or negativelyaffect the safety profile of the battery. Wetting agents or surfactantsmay be added, for example, to allow the electrolyte to wet the separatoror to be filled into the battery package. Again, these wetting agentsmay be positive or negative for safety. The addition of surfactant tothe electrolyte may increase the electrical impedance of the cell,according the lowest concentration of surfactant to achieve the desiredwetting or other properties should be used. Exemplary surfactants mayinclude Triton® X-100, Triton® QS44, and Dowfax® 3B2 in concentrationsfrom 0.01 percent to 2 percent.

One example of an electrolyte formulation may be: 20% zinc chloride, 500ppm of Triton® QS-44, 200 ppm of indium +3 ion supplied as indiumacetate, and the balance water.

Novel electrolytes are also emerging which may dramatically improve thesafety profile of biomedical microbatteries. For example, a class ofsolid electrolytes may be inherently resistant to leaking while stilloffering suitable electrical performance.

Batteries using “salt water” electrolyte are commonly used in reservecells for marine use. Torpedoes, buoys, and emergency lights may usesuch batteries. Reserve cells are batteries in which the activematerials, the electrodes and electrolyte, are separated until the timeof use. Because of this separation, the cells self-discharge is greatlyreduced and shelf life is greatly increased. Salt water batteries may bedesigned from a variety of electrode materials, including zinc,magnesium, aluminum, copper, tin, manganese dioxide, and silver oxide.The electrolyte may be actual sea water, for example, water from theocean flooding the battery upon contact, or may be a speciallyengineered saline formulation. This type of battery may be particularlyuseful in contact lenses. A saline electrolyte may have superiorbiocompatibility as compared to classical electrolytes such as potassiumhydroxide and zinc chloride. Contact lenses are stored in a “packingsolution” which is typically a mixture of sodium chloride, perhaps withother salts and buffering agents. This solution has been demonstrated asa battery electrolyte in combination with a zinc anode and manganesedioxide cathode. Other electrolyte and electrode combinations arepossible. A contact lens using a “salt water” battery may contain anelectrolyte based on sodium chloride, packing solution, or even aspecially engineered electrolyte similar to tear fluid. Such a batterycould, for example, be activated with packing solution, maintain anopening to the eye, and continue operating with exposure to human tears.

In addition to or instead of possible benefits for biocompatibility byusing an electrolyte more similar to tears, or actually using tears, areserve cell may be used to meet the shelf life requirements of acontact lens product. Typical contact lenses are specified for storageof 3 years or more. This is a challenging requirement for a battery witha small and thin package. A reserve cell for use in a contact lens mayhave a design similar to those shown in FIG. 3, but the electrolytewould not be added at the time of manufacture. The electrolyte may bestored in an ampule within the contact lens and connected to thebattery, or saline surrounding the battery may be used as theelectrolyte. Within the contact lens and battery package, a valve orport may be designed to separate the electrolyte from the electrodesuntil the user activates the lens. Upon activation, perhaps by simplypinching the edge of the contact lens similar to activating a glowstick, the electrolyte is allowed to flow into the battery and form anionic pathway between the electrodes. This may involve a one-timetransfer of electrolyte or may expose the battery for continueddiffusion.

Some battery systems may use or consume electrolyte during the chemicalreaction. Accordingly, it may be necessary to engineer a certain volumeof electrolyte into the packaged system. This electrolyte may be“parked” in various locations including the separator or a reservoir.

In some examples, a design of a battery system may include a componentor components that may function to limit discharge capacity of thebattery system. For example, it may be desirable to design the materialsand amounts of materials of the anode, cathode, or electrolyte such thatone of them may be depleted first during the course of reactions in thebattery system. In such an example, the depletion of one of the anode,cathode or electrolyte may reduce the potential for problematicdischarge and side reactions to not take place at lower dischargevoltages. These problematic reactions may produce, for example,excessive gas or byproducts which could be detrimental to safety andother factors.

Modular Battery Components

In some examples, a modular battery component may be formed according tosome aspects and examples of the present disclosure. In these examples,the modular battery assembly may be a separate component from otherparts of the biomedical device. In the example of an ophthalmic contactlens device, such a design may comprise a modular battery that isseparate from the rest of a media insert. There may be numerousadvantages of forming a modular battery component. For example, in theexample of the contact lens, a modular battery component may be formedin a separate, non-integrated process which may alleviate the need tohandle rigid, three-dimensionally formed optical plastic components. Inaddition, the sources of manufacturing may be more flexible and mayoperate in a more parallel mode to the manufacturing of the othercomponents in the biomedical device. Furthermore, the fabrication of themodular battery components may be decoupled from the characteristics ofthree-dimensional shaped devices. For example, in applications requiringthree-dimensional final forms, a modular battery system may befabricated in a flat or roughly two-dimensional perspective and thenshaped to the appropriate three-dimensional shape. A modular batterycomponent may be tested independently of the rest of the biomedicaldevice and yield loss due to battery components may be sorted beforeassembly. The resulting modular battery component may be utilized invarious media insert constructs that do not have an appropriate rigidregion upon which the battery components may be formed; and, in a stillfurther example, the use of modular battery components may facilitatethe use of different options for fabrication technologies than wouldotherwise be utilized, such as web-based technology (roll to roll),sheet-based technology (sheet-to-sheet), printing, lithography, and“squeegee” processing. In some examples of a modular battery, thediscrete containment aspect of such a device may result in additionalmaterial being added to the overall biomedical device construct. Sucheffects may set a constraint for the use of modular battery solutionswhen the available space parameters require minimized thickness orvolume of solutions.

Battery shape requirements may be driven at least in part by theapplication for which the battery is to be used. Traditional batteryform factors may be cylindrical forms or rectangular prisms, made ofmetal, and may be geared toward products which require large amounts ofpower for long durations. These applications may be large enough thatthey may contain large form factor batteries. In another example, planarsolid-state batteries may be thin rectangular prisms, typically formedupon inflexible silicon or glass. These planar solid-state batteries maybe formed in some examples using silicon wafer-processing technologies.In another type of battery form factor, low power, flexible batteriesmay be formed in a pouch construct, using thin foils or plastic tocontain the battery chemistry. These batteries may be made flat, and maybe designed to function when bowed to a modest out-of-plane curvature.

In some of the examples of the battery applications in accordance withthe present invention where the battery may be employed in a variableoptic lens, the form factor may require a three-dimensional curvature ofthe battery component where a radius of that curvature may be on theorder of approximately 8.4 mm. The nature of such a curvature may beconsidered to be relatively steep and for reference may approximate thetype of curvature found on a human fingertip. The nature of a relativesteep curvature creates challenging aspects for manufacture. In someexamples of the present disclosure, a modular battery component may bedesigned such that it may be fabricated in a flat, two-dimensionalmanner and then formed into a three-dimensional form of relative highcurvature.

Battery Module Thickness

In designing battery components for biomedical applications, tradeoffsamongst the various parameters may be made balancing technical, safetyand functional requirements. The thickness of the battery component maybe an important and limiting parameter. For example, in an optical lensapplication the ability of a device to be comfortably worn by a user mayhave a critical dependence on the thickness across the biomedicaldevice. Therefore, there may be critical enabling aspects in designingthe battery for thinner results. In some examples, battery thickness maybe determined by the combined thicknesses of top and bottom sheets,spacer sheets, and adhesive layer thicknesses. Practical manufacturingaspects may drive certain parameters of film thickness to standardvalues in available sheet stock. In addition, the films may have minimumthickness values to which they may be specified base upon technicalconsiderations relating to chemical compatibility, moisture/gasimpermeability, surface finish, and compatibility with coatings that maybe deposited upon the film layers.

In some examples, a desired or goal thickness of a finished batterycomponent may be a component thickness that is less than 220 μm. Inthese examples, this desired thickness may be driven by thethree-dimensional geometry of an exemplary ophthalmic lens device wherethe battery component may need to be fit inside the available volumedefined by a hydrogel lens shape with given end user comfort,biocompatibility, and acceptance constraints. This volume and its effecton the needs of battery component thickness may be a function of totaldevice thickness specification as well as device specification relatingto its width, cone angle, and inner diameter. Another important designconsideration for the resulting battery component design may relate tothe volume available for active battery chemicals and materials in agiven battery component design with respect to the resulting chemicalenergy that may result from that design. This resulting chemical energymay then be balanced for the electrical requirements of a functionalbiomedical device for its targeted life and operating conditions

Battery Module Flexibility

Another dimension of relevance to battery design and to the design ofrelated devices that utilize battery based energy sources is theflexibility of the battery component. There may be numerous advantagesconferred by flexible battery forms. For example, a flexible batterymodule may facilitate the previously mentioned ability to fabricate thebattery form in a two-dimensional flat form. The flexibility of the formmay allow the two-dimensional battery to then be formed into anappropriate three-dimensional shape to fit into a biomedical device suchas a contact lens.

In another example of the benefits that may be conferred by flexibilityin the battery module, if the battery and the subsequent device isflexible then there may be advantages relating to the use of the device.In an example, a contact lens form of a biomedical device may haveadvantages for insertion/removal of the media insert based contact lensthat may be closer to the insertion/removal of a standard, non-filledhydrogel contact lens.

The number of flexures may be important to the engineering of thebattery. For example, a battery which may only flex one time from aplanar form into a shape suitable for a contact lens may havesignificantly different design from a battery capable of multipleflexures. The flexure of the battery may also extend beyond the abilityto mechanically survive the flexure event. For example, an electrode maybe physically capable of flexing without breaking, but the mechanicaland electrochemical properties of the electrode may be altered byflexure. Flex-induced changes may appear instantly, for example, aschanges to impedance, or flexure may introduce changes which are onlyapparent in long-term shelf life testing.

Battery Module Width

There may be numerous applications into which the biocompatibleenergization elements or batteries of the present disclosure may beutilized. In general, the battery width requirement may be largely afunction of the application in which it is applied. In an exemplarycase, a contact lens battery system may have constrained needs for thespecification on the width of a modular battery component. In someexamples of an ophthalmic device where the device has a variable opticfunction powered by a battery component, the variable optic portion ofthe device may occupy a central spherical region of about 7.0 mm indiameter. The exemplary battery elements may be considered as a3-dimensional object, which fits as an annular, conical skirt around thecentral optic and formed into a truncated conical ring. If the requiredmaximum diameter of the rigid insert is a diameter of 8.50 mm, andtangency to a certain diameter sphere may be targeted (as for example ina roughly 8.40 mm diameter), then geometry may dictate what theallowable battery width may be. There may be geometric models that maybe useful for calculating desirable specifications for the resultinggeometry which in some examples may be termed a conical frustumflattened into a sector of an annulus.

Flattened battery width may be driven by two features of the batteryelement, the active battery components and seal width. In some examplesrelating to ophthalmic devices a target thickness may be between 0.100mm and 0.500 mm per side, and the active battery components may betargeted at roughly 0.800 mm wide. Other biomedical devices may havediffering design constraints but the principles for flexible flatbattery elements may apply in similar fashion.

Cavities as Design Elements in Battery Component Design

In some examples, battery elements may be designed in manners thatsegment the regions of active battery chemistry. There may be numerousadvantages from the division of the active battery components intodiscrete segments. In a non-limiting example, the fabrication ofdiscrete and smaller elements may facilitate production of the elements.The function of battery elements including numerous smaller elements maybe improved. Defects of various kinds may be segmented andnon-functional elements may be isolated in some cases to result indecreased loss of function. This may be relevant in examples where theloss of battery electrolyte may occur. The isolation of individualizedcomponents may allow for a defect that results in leakage of electrolyteout of the critical regions of the battery to limit the loss of functionto that small segment of the total battery element whereas theelectrolyte loss through the defect could empty a significantly largerregion for batteries configured as a single cell. Smaller cells mayresult in lowered volume of active battery chemicals on an overallperspective, but the mesh of material surrounding each of the smallercells may result in a strengthening of the overall structure.

Battery Element Internal Seals

In some examples of battery elements for use in biomedical devices, thechemical action of the battery involves aqueous chemistry, where wateror moisture is an important constituent to control. Therefore it may beimportant to incorporate sealing mechanisms that retard or prevent themovement of moisture either out of or into the battery body. Moisturebarriers may be designed to keep the internal moisture level at adesigned level, within some tolerance. In some examples, a moisturebarrier may be divided into two sections or components; namely, thepackage and the seal.

The package may refer to the main material of the enclosure. In someexamples, the package may be comprised of a bulk material. The WaterVapor Transmission Rate (WVTR) may be an indicator of performance, withISO, ASTM standards controlling the test procedure, including theenvironmental conditions operant during the testing. Ideally, the WVTRfor a good battery package may be “zero.” Exemplary materials with anear-zero WVTR may be glass and metal foils. Plastics, on the otherhand, may be inherently porous to moisture, and may vary significantlyfor different types of plastic. Engineered materials, laminates, orco-extrudes may usually be hybrids of the common package materials.

The seal may be the interface between two of the package surfaces. Theconnecting of seal surfaces finishes the enclosure along with thepackage. In many examples, the nature of seal designs may make themdifficult to characterize for the seal's WVTR due to difficulty inperforming measurements using an ISO or ASTM standard, as the samplesize or surface area may not be compatible with those procedures. Insome examples, a practical manner to testing seal integrity may be afunctional test of the actual seal design, for some defined conditions.Seal performance may be a function of the seal material, the sealthickness, the seal length, the seal width, and the seal adhesion orintimacy to package substrates.

In some examples, seals may be formed by a welding process that mayinvolve thermal, laser, solvent, friction, ultrasonic, or arcprocessing. In other examples, seals may be formed through the use ofadhesive sealants such as glues, epoxies, acrylics, natural rubber, andsynthetic rubber. Other examples may derive from the utilization ofgasket type material that may be formed from cork, natural and syntheticrubber, polytetrafluoroethylene (PTFE), polypropylene, and silicones tomention a few non-limiting examples.

In some examples, the batteries according to the present disclosure maybe designed to have a specified operating life. The operating life maybe estimated by determining a practical amount of moisture permeabilitythat may be obtained using a particular battery system and thenestimating when such a moisture leakage may result in an end of lifecondition for the battery. For example, if a battery is stored in a wetenvironment, then the partial pressure difference between inside andoutside the battery will be minimal, resulting in a reduced moistureloss rate, and therefore the battery life may be extended. The sameexemplary battery stored in a particularly dry and hot environment mayhave a significantly reduced expectable lifetime due to the strongdriving function for moisture loss.

Battery Element Separators

Batteries of the type described in the present disclosure may utilize aseparator material that physically and electrically separates the anodeand anode current collector portions from the cathode and cathodecurrent collector portions. The separator may be a membrane that ispermeable to water and dissolved electrolyte components; however, it maytypically be electrically non-conductive. While a myriad ofcommercially-available separator materials may be known to those ofskill in the art, the novel form factor of the present disclosure maypresent unique constraints on the task of separator selection,processing, and handling.

Since the designs of the present disclosure may have ultra-thinprofiles, the choice may be limited to the thinnest separator materialstypically available. For example, separators of approximately 25 micronsin thickness may be desirable. Some examples which may be advantageousmay be about 12 microns in thickness. There may be numerous acceptablecommercial separators include microfibrillated, microporous polyethylenemonolayer and/or polypropylene-polyethylene-polypropylene (PP/PE/PP)trilayer separator membranes such as those produced by Celgard(Charlotte, N.C.). A desirable example of separator material may beCelgard M824 PP/PE/PP trilayer membrane having a thickness of 12microns. Alternative examples of separator materials useful for examplesof the present invention may include separator membranes comprisingregenerated cellulose (e.g. cellophane).

While PP/PE/PP trilayer separator membranes may have advantageousthickness and mechanical properties, owing to their polyolefiniccharacter, they may also suffer from a number of disadvantages that mustbe overcome in order to make them useful in examples of the presentinvention. Roll or sheet stock of PP/PE/PP trilayer separator materialsmay have numerous wrinkles or other form errors that may be deleteriousto the micron-level tolerances applicable to the batteries describedherein. Furthermore, polyolefin separators may need to be cut toultra-precise tolerances for inclusion in the present designs, which maytherefore implicate laser cutting as a preferred method of formingdiscrete current collectors in desirable shapes with tight tolerances.Owing to the polyolefinic character of these separators, certain cuttinglasers useful for micro fabrication may employ laser wavelengths, e.g.355 nm, that will not cut polyolefins. The polyolefins do notappreciably absorb the laser energy and are thereby non-ablatable.Finally, polyolefin separators may not be inherently wettable to aqueouselectrolytes used in the batteries described herein.

Nevertheless, there may be methods for overcoming these inherentlimitations for polyolefinic type membranes. In order to present amicroporous separator membrane to a high-precision cutting laser forcutting pieces into arc segments or other advantageous separatordesigns, the membrane may need to be flat and wrinkle-free. If these twoconditions are not met, the separator membrane may not be fully cutbecause the cutting beam may be inhibited as a result of defocusing ofor otherwise scattering the incident laser energy. Additionally, if theseparator membrane is not flat and wrinkle-free, the form accuracy andgeometric tolerances of the separator membrane may not be sufficientlyachieved. Allowable tolerances for separators of current examples may bepreferably +0 microns and −20 microns with respect to characteristiclengths and/or radii. There may be advantages for tighter tolerances of+0 microns and −10 micron and further for tolerances of +0 microns and−5 microns. Separator stock material may be made flat and wrinkle-freeby temporarily laminating the material to a float glass carrier with anappropriate low-volatility liquid. Low-volatility liquids may bepreferred over temporary adhesives due to the fragility of the separatormembrane and due to the amount of processing time that may be requiredto release separator membrane from an adhesive layer. Furthermore, insome examples achieving a flat and wrinkle-free separator membrane onfloat glass using a liquid has been observed to be much more facile thanusing an adhesive. Prior to lamination, the separator membrane may bemade free of particulates. This may be achieved by ultrasonic cleaningof separator membrane to dislodge any surface-adherent particulates. Insome examples, handling of a separator membrane may be done in asuitable, low-particle environment such as a laminar flow hood or acleanroom of at least class 10,000. Furthermore, the float glasssubstrate may be made to be particulate free by rinsing with anappropriate solvent, ultrasonic cleaning, and/or wiping with clean roomwipes.

While a wide variety of low-volatility liquids may be used for themechanical purpose of laminating microporous polyolefin separatormembranes to a float glass carrier, specific requirements may be imposedon the liquid to facilitate subsequent laser cutting of discreteseparator shapes. One requirement may be that the liquid has a surfacetension low enough to soak into the pores of the separator materialwhich may easily be verified by visual inspection. In some examples, theseparator material turns from a white color to a translucent appearancewhen liquid fills the micropores of the material. It may be desirable tochoose a liquid that may be benign and “safe” for workers that will beexposed to the preparation and cutting operations of the separator. Itmay be desirable to choose a liquid whose vapor pressure may be lowenough so that appreciable evaporation does not occur during the timescale of processing (on the order of 1 day). Finally, in some examplesthe liquid may have sufficient solvating power to dissolve advantageousUV absorbers that may facilitate the laser cutting operation. In anexample, it has been observed that a 12 percent (w/w) solution ofavobenzone UV absorber in benzyl benzoate solvent may meet theaforementioned requirements and may lend itself to facilitating thelaser cutting of polyolefin separators with high precision and tolerancein short order without an excessive number of passes of the cuttinglaser beam. In some examples, separators may be cut with an 8W 355 nmnanosecond diode-pumped solid state laser using this approach where thelaser may have settings for low power attenuation (e.g. 3 percentpower), a moderate speed of 1 to 10 mm/s, and only 1 to 3 passes of thelaser beam. While this UV-absorbing oily composition has been proven tobe an effective laminating and cutting process aid, other oilyformulations may be envisaged by those of skill in the art and usedwithout limitation.

In some examples, a separator may be cut while fixed to a float glass.One advantage of laser cutting separators while fixed to a float glasscarrier may be that a very high number density of separators may be cutfrom one separator stock sheet; much like semiconductor die may bedensely arrayed on a silicon wafer. Such an approach may provide economyof scale and parallel processing advantages inherent in semiconductorprocesses. Furthermore, the generation of scrap separator membrane maybe minimized. Once separators have been cut, the oily process aid fluidmay be removed by a series of extraction steps with miscible solvents,the last extraction may be performed with a high-volatility solvent suchas isopropyl alcohol in some examples. Discrete separators, onceextracted, may be stored indefinitely in any suitable low-particleenvironment.

As previously set forth, polyolefin separator membranes may beinherently hydrophobic and may need to be made wettable to aqueoussurfactants used in the batteries of the present invention. One approachto make the separator membranes wettable may be oxygen plasma treatment.For example, separators may be treated for 1 to 5 minutes in a 100percent oxygen plasma at a wide variety of power settings and oxygenflow rates. While this approach may improve wettability for a time, itmay be well-known that plasma surface modifications provide a transienteffect that may not last long enough for robust wetting of electrolytesolutions. Another approach to improve wettability of separatormembranes may be to treat the surface by incorporating a suitablesurfactant on the membrane. In some cases, the surfactant may be used inconjunction with a hydrophilic polymeric coating that remains within thepores of the separator membrane.

Another approach to provide more permanence to the hydrophilicityimparted by an oxidative plasma treatment may be by subsequent treatmentwith a suitable hydrophilic organosilane. In this manner, the oxygenplasma may be used to activate and impart functional groups across theentire surface area of the microporous separator. The organosilane maythen covalently bond to and/or non-covalently adhere to the plasmatreated surface. In examples using an organosilane, the inherentporosity of the microporous separator may not be appreciably changed;monolayer surface coverage may also be possible and desired. Prior artmethods incorporating surfactants in conjunction with polymeric coatingsmay require stringent controls over the actual amount of coating appliedto the membrane, and may then be subject to process variability. Inextreme cases, pores of the separator may become blocked, therebyadversely affecting utility of the separator during the operation of theelectrochemical cell. An exemplary organosilane useful in the presentdisclosure may be (3-aminopropyl)triethoxysilane. Other hydrophilicorganosilanes may be known to those of skill in the art and may be usedwithout limitation.

Still another method for making separator membranes wettable by aqueouselectrolyte may be the incorporation of a suitable surfactant in theelectrolyte formulation. One consideration in the choice of surfactantfor making separator membranes wettable may be the effect that thesurfactant may have on the activity of one or more electrodes within theelectrochemical cell, for example, by increasing the electricalimpedance of the cell. In some cases, surfactants may have advantageousanti-corrosion properties, specifically in the case of zinc anodes inaqueous electrolytes. Zinc may be an example known to undergo a slowreaction with water to liberate hydrogen gas, which may be undesirable.Numerous surfactants may be known by those of skill in the art to limitrates of said reaction to advantageous levels. In other cases, thesurfactant may so strongly interact with the zinc electrode surface thatbattery performance may be impeded. Consequently, much care may need tobe made in the selection of appropriate surfactant types and loadinglevels to ensure that separator wettability may be obtained withoutdeleteriously affecting electrochemical performance of the cell. In somecases, a plurality of surfactants may be used, one being present toimpart wettability to the separator membrane and the other being presentto facilitate anti-corrosion properties to the zinc anode. In oneexample, no hydrophilic treatment is done to the separator membrane anda surfactant or plurality of surfactants is added to the electrolyteformulation in an amount sufficient to effect wettability of theseparator membrane.

Discrete separators may be integrated into the laminar microbattery bydirect placement into a designed cavity, pocket, or structure within theassembly. Desirably, this pocket may be formed by a spacer having acutout that may be a geometric offset of the separator shape.Furthermore, the pocket may have a ledge or step on which the separatorrests during assembly. Said ledge or step may optionally include apressure sensitive adhesive which retains the discrete separator.Advantageously, the pressure sensitive adhesive may be the same one usedin the construction and stack up of other elements of an exemplarylaminar microbattery.

Pressure Sensitive Adhesive

In some examples, the plurality of components comprising the laminarmicrobatteries of the present invention may be held together with apressure-sensitive adhesive (PSA) that also serves as a sealant. While amyriad of commercially available pressure sensitive adhesiveformulations may exist, such formulations almost always includecomponents that may make them unsuitable for use within a biocompatiblelaminar microbattery. Examples of undesirable components in pressuresensitive adhesives may include: low molecular mass leachablecomponents, antioxidants e.g. BHT and/or MEHQ, plasticizing oils,impurities, oxidatively unstable moieties containing, for example,unsaturated chemical bonds, residual solvents and/or monomers,polymerization initiator fragments, polar tackifiers, and the like.

Suitable PSAs may on the other hand exhibit the following properties.They may be able to be applied to laminar components to achieve thinlayers on the order of 2 to 20 microns. As well, they may contain aminimum of, preferably zero, undesirable or non-biocompatiblecomponents. Additionally, they may have sufficient adhesive and cohesiveproperties so as to bind the components of the laminar battery together.And, they may be able to flow into the micron-scale features inherent indevices of the present construction while providing for a robust sealingof electrolyte within the battery. In some examples of suitable PSAs,the PSAs may have a low permeability to water vapor in order to maintaina desirable aqueous electrolyte composition within the battery even whenthe battery may be subjected to extremes in humidity for extendedperiods of time. The PSAs may have good chemical resistance tocomponents of electrolytes such as acids, surfactants, and salts. Theymay be inert to the effects of water immersion. Suitable PSAs may have alow permeability to oxygen to minimize the rate of direct oxidation,which may be a form of self-discharge, of zinc anodes. And, they mayfacilitate a finite permeability to hydrogen gas, which may be slowlyevolved from zinc anodes in aqueous electrolytes. This property offinite permeability to hydrogen gas may avoid a build-up of internalpressure.

In consideration of these requirements, polyisobutylene (PIB) may be acommercially-available material that may be formulated into PSAcompositions meeting many if not all desirable requirements.Furthermore, PIB may be an excellent barrier sealant with very low waterabsorbance and low oxygen permeability. An example of PIB useful in theexamples of the present invention may be Oppanol® B15 by BASFCorporation. Oppanol® B15 may be dissolved in hydrocarbon solvents suchas toluene, heptane, dodecane, mineral spirits, and the like. Oneexemplary PSA composition may include 30 percent Oppanol® B15 (w/w) in asolvent mixture including 70 percent (w/w) toluene and 30 percentdodecane. The adhesive and rheological properties of PIB based PSA's maybe determined in some examples by the blending of different molecularmass grades of PIB. A common approach may be to use a majority of lowmolar mass PIB, e.g. Oppanol® B10 to affect wetting, tack, and adhesion,and to use a minority of high molar mass PIB to affect toughness andresistance to flow. Consequently, blends of any number of PIB molar massgrades may be envisioned and may be practiced within the scope of thepresent invention. Furthermore, tackifiers may be added to the PSAformulation so long as the aforementioned requirements may be met. Bytheir very nature, tackifiers impart polar properties to PSAformulations, so they may need to be used with caution so as to notadversely affect the barrier properties of the PSA. Furthermore,tackifiers may in some cases be oxidatively unstable and may include anantioxidant, which could leach out of the PSA. For these reasons,exemplary tackifiers for use in PSA's for biocompatible laminarmicrobatteries may include fully- or mostly hydrogenated hydrocarbonresin tackifiers such as the Regalrez series of tackifiers from EastmanChemical Corporation.

Additional Package and Substrate considerations in Biocompatible BatteryModules

There may be numerous packaging and substrate considerations that maydictate desirable characteristics for package designs used inbiocompatible laminar microbatteries. For example, the packaging maydesirably be predominantly foil and/or film based where these packaginglayers may be as thin as possible, for example, 10 to 50 microns.Additionally, the packaging may provide a sufficient diffusion barrierto moisture gain or loss during the shelf life. In many desirableexamples, the packaging may provide a sufficient diffusion barrier tooxygen ingress to limit degradation of zinc anodes by direct oxidation.

In some examples, the packaging may provide a finite permeation pathwayto hydrogen gas that may evolve due to direct reduction of water byzinc. And, the packaging may desirably sufficiently contain and mayisolate the contents of the battery such that potential exposure to auser may be minimized.

In the present disclosure, packaging constructs may comprise thefollowing types of functional components; namely, top and bottompackaging layers, PSA layers, spacer layers, interconnect zones, fillingports, and secondary packaging.

In some examples, top and bottom packaging layers may comprise metallicfoils or polymer films. Top and bottom packaging layers may comprisemulti-layer film constructs containing a plurality of polymer and/orbarrier layers. Such film constructs may be referred to as coextrudedbarrier laminate films. An example of a commercial coextruded barrierlaminate film of particular utility in the present invention may be 3MScotchpak 1109 backing which consists of a PET carrier web, avapor-deposited aluminum barrier layer, and a polyethylene layercomprising a total average film thickness of 33 microns. Numerous othersimilar multilayer barrier films may be available and may be used inalternate examples of the present invention.

In design constructions comprising a PSA, packaging layer surfaceroughness may be of particular importance, because the PSA may also needto seal opposing packaging layer faces. Surface roughness may resultfrom manufacturing processes used in foil and film production, forexample, processes employing rolling, extruding, embossing and/orcalendaring, among others. If the surface is too rough, PSA may be notable to be applied in a uniform thickness when the desired PSA thicknessmay be on the order of the surface roughness Ra (the arithmetic averageof the roughness profile). Furthermore, PSA's may not adequately sealagainst an opposing face if the opposing face has roughness that may beon the order of the PSA layer thickness. In the present disclosure,packaging materials having a surface roughness, Ra, less than 10 micronsmay be acceptable examples. In some examples, surface roughness valuesmay be 5 microns or less. And, in still further examples, the surfaceroughness may be 1 micron or less. Surface roughness values may bemeasured by a variety of methods including but not limited tomeasurement techniques such as white light interferometry, stylusprofilometry, and the like. There may be many examples in the art ofsurface metrology that surface roughness may be described by a number ofalternative parameters and that the average surface roughness, Ra,values discussed herein may be meant to be representative of the typesof features inherent in the aforementioned manufacturing processes.

Current Collectors and Electrodes

In some examples of zinc-carbon and Leclanché cells, the cathode currentcollector may be a sintered carbon rod. This type of material may facetechnical hurdles for thin electrochemical cells of the presentdisclosure. In some examples, printed carbon inks may be used in thinelectrochemical cells to replace a sintered carbon rod for the cathodecurrent collector, and in these examples, the resulting device may beformed without significant impairment to the resulting electrochemicalcell. Typically, said carbon inks may be applied directly to packagingmaterials which may comprise polymer films, or in some cases metalfoils. In the examples where the packaging film may be a metal foil, thecarbon ink may need to protect the underlying metal foil from chemicaldegradation and/or corrosion by the electrolyte. Furthermore, in theseexamples, the carbon ink current collector may need to provideelectrical conductivity from the inside of the electrochemical cell tothe outside of the electrochemical cell, implying sealing around orthrough the carbon ink. Due to the porous nature of carbon inks, thismay be not easily accomplished without significant challenges. Carboninks also may be applied in layers that have finite and relatively smallthickness, for example, 10 to 20 microns. In a thin electrochemical celldesign in which the total internal package thickness may only be about100 to 150 microns, the thickness of a carbon ink layer may take up asignificant fraction of the total internal volume of the electrochemicalcell, thereby negatively impacting electrical performance of the cell.Further, the thin nature of the overall battery and the currentcollector in particular may imply a small cross-sectional area for thecurrent collector. As resistance of a trace increases with trace lengthand decreases with cross-section, there may be a direct tradeoff betweencurrent collector thickness and resistance. The bulk resistivity ofcarbon ink may be insufficient to meet the resistance requirement ofthin batteries Inks filled with silver or other conductive metals mayalso be considered to decrease resistance and/or thickness, but they mayintroduce new challenges such as incompatibility with novelelectrolytes. In consideration of these factors, in some examples it maybe desirable to realize efficient and high performance thinelectrochemical cells of the present disclosure by utilizing a thinmetal foil as the current collector, or to apply a thin metal film to anunderlying polymer packaging layer to act as the current collector. Suchmetal foils may have significantly lower resistivity, thereby allowingthem to meet electrical resistance requirements with much less thicknessthan printed carbon inks.

In some examples, one or more of the top and/or bottom packaging layersmay serve as a substrate for a sputtered current collector metal ormetal stack. For example, 3M Scotchpak 1109 backing may be metallizedusing physical vapor deposition (PVD) of one or more metallic layersuseful as a current collector for a cathode. Example metal stacks usefulas cathode current collectors may be Ti—W (titanium-tungsten) adhesionlayers and Ti (titanium) conductor layers. Exemplary metal stacks usefulas anode current collectors may be Ti—W adhesion layers, Au (gold)conductor layers, and In (indium) deposition layers. The thickness ofthe PVD layers may be preferably less than 500 nm in total. If multiplelayers of metals are used, the electrochemical and barrier propertiesmay need to be compatible with the battery. For example, copper may beelectroplated on top of a seed layer to grow a thick layer of conductor.Additional layers may be plated upon the copper. However, copper may beelectrochemically incompatible with certain electrolytes especially inthe presence of zinc. Accordingly, if copper is used as a layer in thebattery, it may need to be sufficiently isolated from the batteryelectrolyte. Alternatively, copper may be excluded or another metalsubstituted.

In some other examples, top and/or bottom packaging foils may alsofunction as current collectors. For example, a 25 micron brass foil maybe useful as an anode current collector for a zinc anode. The brass foilmay be optionally electroplated with indium prior to electroplating withzinc. In a preferred embodiment, cathode current collector packagingfoils may comprise titanium foil, Hastelloy C-276 foil, chromium foil,and/or tantalum foil. In certain designs, one or more packaging foilsmay be fine blanked, embossed, etched, textured, laser machined, orotherwise processed to provide desirable form, surface roughness, and/orgeometry to the final cell packaging.

Anode and Anode Corrosion Inhibitors

The anode for the laminar battery of the present invention maypreferentially comprise zinc. In traditional zinc carbon batteries, azinc anode may take the physical form of a can in which the contents ofthe electrochemical cell may be contained. For the battery of thepresent disclosure, a zinc can may be an example, but there may be otherphysical forms of zinc that may provide desirable to realize ultra-smallbattery designs.

Electroplated zinc may have examples of use in a number of industries,for example, for the protective or aesthetic coating of metal parts. Insome examples, electroplated zinc may be used to form thin and conformalanodes useful for batteries of the present invention. Furthermore, theelectroplated zinc may be patterned in seemingly endless configurations,depending on the design intent. A facile means for patterningelectroplated zinc may be processing with the use of a photomask or aphysical mask. A plating mask may be fabricated by a variety ofapproaches. One approach may be by using a photomask. In these examples,a photoresist may be applied to a conductive substrate, the substrate onwhich zinc may subsequently be plated. The desired plating pattern maybe then projected to the photoresist by means of a photomask, therebycausing curing of selected areas of photoresist. The uncured photoresistmay then be removed with appropriate solvent and cleaning techniques.The result may be a patterned area of conductive material that canreceive an electroplated zinc treatment. While this method may providebenefit to the shape or design of the zinc to be plated, the approachmay require use of available photo-patternable materials, which may haveconstrained properties to the overall cell package construction.Consequently, new and novel methods for patterning zinc may be requiredto realize some designs of thin microbatteries of the presentdisclosure.

An alternative means of patterning zinc anodes may be by means of aphysical mask application. A physical mask may be made by cuttingdesirable apertures in a film having desirable barrier and/or packagingproperties. Additionally, the film may have pressure sensitive adhesiveapplied to one or both sides. Finally, the film may have protectiverelease liners applied to one or both adhesives. The release liner mayserve the dual purpose of protecting the adhesive during aperturecutting and protecting the adhesive during specific processing steps ofassembling the electrochemical cell, specifically the cathode fillingstep, described in following description. In some examples, a zinc maskmay comprise a PET film of approximately 100 microns thickness to whicha pressure sensitive adhesive may be applied to both sides in a layerthickness of approximately 10-20 microns. Both PSA layers may be coveredby a PET release film which may have a low surface energy surfacetreatment, and may have an approximate thickness of 50 microns. In theseexamples, the multi-layer zinc mask may comprise PSA and PET film. PETfilms and PET/PSA zinc mask constructs as described herein may bedesirably processed with precision nanosecond laser micromachiningequipment, such as an Oxford Lasers E-Series laser micromachiningworkstation, to create ultra-precise apertures in the mask to facilitateplating. In essence, once the zinc mask has been fabricated, one side ofthe release liner may be removed, and the mask with apertures may belaminated to the anode current collector and/or anode-side packagingfilm/foil. In this manner, the PSA creates a seal at the inside edges ofthe apertures, facilitating clean and precise masking of the zinc duringelectroplating.

The zinc mask may be placed and then electroplating of one or moremetallic materials may be performed. In some examples, zinc may beelectroplated directly onto an electrochemically compatible anodecurrent collector foil such as brass. In alternate design examples wherethe anode side packaging comprises a polymer film or multi-layer polymerfilm upon which seed metallization has been applied, zinc, and/or theplating solutions used for depositing zinc, may not be chemicallycompatible with the underlying seed metallization. Manifestations oflack of compatibility may include film cracking, corrosion, and/orexacerbated H₂ evolution upon contact with cell electrolyte. In such acase, additional metals may be applied to the seed metal to affectbetter overall chemical compatibility in the system. One metal that mayfind particular utility in electrochemical cell constructions may beindium. Indium may be widely used as an alloying agent in battery gradezinc with its primary function being to provide an anti-corrosionproperty to the zinc in the presence of electrolyte. In some examples,indium may be successfully deposited on various seed metallizations suchas Ti—W and Au. Resulting films of 1-3 microns of indium on said seedmetallization layers may be low-stress and adherent. In this manner, theanode-side packaging film and attached current collector having anindium top layer may be conformable and durable. In some examples, itmay be possible to deposit zinc on an indium-treated surface, theresulting deposit may be very non-uniform and nodular. This effect mayoccur at lower current density settings, for example, 20 amps per squarefoot (ASF). As viewed under a microscope, nodules of zinc may beobserved to form on the underlying smooth indium deposit. In certainelectrochemical cell designs, the vertical space allowance for the zincanode layer may be up to about 5-10 microns maximum, but in someexamples, lower current densities may be used for zinc plating, and theresulting nodular growths may grow taller than the maximum anodevertical allowance. It may be that the nodular zinc growth stems from acombination of the high overpotential of indium and the presence of anoxide layer of indium.

In some examples, higher current density DC plating may overcome therelatively large nodular growth patterns of zinc on indium surfaces. Forexample, 100 ASF plating conditions may result in nodular zinc, but thesize of the zinc nodules may be drastically reduced compared to 20 ASFplating conditions. Furthermore, the number of nodules may be vastlygreater under 100 ASF plating conditions. The resulting zinc film mayultimately coalesce to a more or less uniform layer with only someresidual feature of nodular growth while meeting the vertical spaceallowance of about 5-10 microns.

An added benefit of indium in the electrochemical cell may be reductionof hydrogen gas, which may be a slow process that occurs in aqueouselectrochemical cells containing zinc. The indium may be beneficiallyapplied to one or more of the anode current collector, the anode itselfas a co-plated alloying component, or as a surface coating on theelectroplated zinc. For the latter case, indium surface coatings may bedesirably applied in-situ by way of an electrolyte additive such asindium trichloride or indium acetate. When such additives may be addedto the electrolyte in small concentrations, indium may spontaneouslyplate on exposed zinc surfaces as well as portions of exposed anodecurrent collector.

Zinc and similar anodes commonly used in commercial primary batteries istypically found in sheet, rod, and paste forms. The anode of aminiature, biocompatible battery may be of similar form, e.g. thin foil,or may be plated as previously mentioned. The properties of this anodemay differ significantly from those in existing batteries, for example,because of differences in contaminants or surface finish attributed tomachining and plating processes. Accordingly, the electrodes andelectrolyte may require special engineering to meet capacity, impedance,and shelf life requirements. For example, special plating processparameters, plating bath composition, surface treatment, and electrolytecomposition may be needed to optimize electrode performance.

Cathode Mix

There may be numerous cathode chemistry mixes that may be consistentwith the concepts of the present disclosure. In some examples, a cathodemix, which may be a term for a chemical formulation used to form abattery's cathode, may be applied as a paste or slurry and may comprisemanganese dioxide, some form of conductive carbon such as carbon blackor graphite, and other optional components. In some examples, theseoptional components may comprise one or more of binders, electrolytesalts, corrosion inhibitors, water or other solvents, surfactants,rheology modifiers, and other conductive additives such as conductivepolymers. Once formulated and appropriately mixed, the cathode mix mayhave a desirable rheology that allows it to either be dispensed ontodesired portions of the separator and/or cathode current collector, orsqueegeed through a screen or stencil in a similar manner. In someexamples, the cathode mix may be dried prior to later cell assemblysteps, while in other examples, the cathode may contain some or all ofthe electrolyte components, and may only be partially dried to aselected moisture content.

The manganese dioxide which may be used in the cathode mix may bepreferably electrolytic manganese dioxide (EMD) due to the beneficialadditional energy capacity that this type of manganese dioxide providesrelative to other forms, such as, natural manganese dioxide or chemicalmanganese dioxide. Furthermore, the EMD useful in batteries of thepresent invention may need to have a particle size and particle sizedistribution that may be conducive to the formation of depositable orprintable cathode mix pastes/slurries. Specifically, the EMD may beprocessed to remove significant large particulate components that wouldbe considered large relative to other features such as battery internaldimensions, separator thicknesses, dispense tip diameters, stencilopening sizes, or screen mesh sizes. In some examples, EMD may have anaverage particle size of 7 microns with a large particle content thatmay contain particulates up to about 70 microns. In alternativeexamples, the EMD may be sieved, further milled, or otherwise separatedor processed to limit large particulate content to below a certainthreshold, for example, 25 microns or smaller. One process useful forthe particle size reduction of EMD may be jet milling where sub-micronparticulate may be obtained. Other processes useful for large particlesize reduction may include ball milling or 3-roll milling of the cathodemix paste prior to use.

A critical aspect of the cathode mix paste may be the polymeric binder.The binder may serve a number of functions in the cathode mix paste. Theprimary function of the binder may be to create a sufficientinter-particle electrical network between EMD particles and carbonparticles. A secondary function of the binder may be to facilitateelectrical contact to the cathode current collector. A third function ofthe binder may be to influence the rheological properties of the cathodemix paste for advantageous dispensing and/or stenciling/screening.Still, a fourth function of the binder may be to enhance the electrolyteuptake and distribution within the cathode. The choice of the binderpolymer as well as the specific amount to be used may be critical to thebeneficial function of the cathode in the electrochemical cell of thepresent disclosure. If the binder polymer is too soluble in theelectrolyte to be used, then the primary function of the binder,electrical continuity, may be drastically impacted to the point of cellnon-functionality. On the contrary, if the binder polymer is insolublein the electrolyte to be used, portions of EMD may be ionicallyinsulated from the electrolyte, resulting in diminished cell performancesuch as reduced capacity, lower open circuit voltage, and/or increasedinternal resistance. In the end, choice of binder polymer and amount tobe used may be a careful balancing act that may need to be determined bycareful experimentation, in some examples using the “design ofexperiments” approach. Examples of binder polymers useful for thepresent disclosure comprise polyvinylpyrrolidone, polyisobutylene,rubbery triblock copolymers comprising styrene end blocks such as thosemanufactured by Kraton Polymers, styrene-butadiene latex blockcopolymers, polyacrylic acid, hydroxyethylcellulose,carboxymethylcellulose, among others.

The cathode may also comprise silver dioxide or nickel oxyhydroxideamong other candidate materials. Such materials may offer increasedcapacity and less decrease in loaded voltage during discharge relativeto manganese dioxide, both desirable properties in a battery. Batteriesbased on these cathodes may have current examples present in industryand literature. A novel microbattery utilizing a silver dioxide cathodemay include a biocompatible electrolyte, for example, one comprisingzinc chloride and/or ammonium chloride instead of potassium hydroxide.

Battery Architecture and Fabrication

Battery architecture and fabrication technology may be closelyintertwined. As has been discussed in earlier sections of thespecification, a battery has the following elements: cathode, anode,separator, electrolyte, cathode current collector, anode currentcollector, and packaging. Clever design may try to combine theseelements in easy to fabricate subassemblies. In other examples,optimized design may have dual-use components, such as using a metalpackage to double as a current collector. From a relative volume andthickness standpoint, these elements may be nearly all the same volume,except for the cathode. In some examples, the electrochemical system mayrequire about two (2) to ten (10) times the volume of cathode as anodedue to significant differences in mechanical density, energy density,discharge efficiency, material purity, and the presence of binders,fillers, and conductive agents. In these examples, the relative scale ofthe various components may be approximated in the following thicknessesof the elements: Anode current collector=1 μm; Cathode currentcollector=1 μm; Electrolyte=interstitial liquid (effectively 0 μm);Separator=as thin or thick as desired where the planned maximalthickness may be approximately 15 μm; Anode=5 μm; and the Cathode=50 μm.For these examples of elements the packaging needed to providesufficient protection to maintain battery chemistry in use environmentsmay have a planned maximal thickness of approximately 50 μm.

In some examples, which may be fundamentally different from large,prismatic constructs such as cylindrical or rectangular forms and whichmay be different than wafer-based solid state construct, such examplesmay assume a “pouch”-like construct, using webs or sheets fabricatedinto various configurations, with battery elements arranged inside. Thecontainment may have two films or one film bent over onto the other sideeither configuration of which may form two roughly planar surfaces,which may be then sealed on the perimeter to form a container. Thisthin-but-wide form factor may make battery elements themselves thin andwide. Furthermore, these examples may be suitable for applicationthrough coating, gravure printing, screen printing, sputtering, or othersimilar fabrication technology.

There may be numerous arrangements of the internal components, such asthe anode, separator and cathode, in these “pouch-like” battery exampleswith thin-but-wide form factor. Within the enclosed region formed by thetwo films, these basic elements may be either “co-planar” that isside-by-side on the same plane or “co-facial” which may be face-to-faceon opposite planes. In the co-planar arrangement, the anode, separator,and cathode may be deposited on the same surface. For the co-facialarrangement, the anode may be deposited on surface-1, the cathode may bedeposited on surface-2, and the separator may be placed between the two,either deposited on one of the sides, or inserted as its own separateelement.

Another type of example may be classified as laminate assembly, whichmay involve using films, either in a web or sheet form, to build up abattery layer by layer. Sheets may be bonded to each other usingadhesives, such as pressure sensitive adhesives, thermally activatedadhesives, or chemical reaction-based adhesives. In some examples thesheets may be bonded by welding techniques such as thermal welding,ultrasonic welding and the like. Sheets may lend themselves to standardindustry practices as roll-to-roll (R2R), or sheet-to-sheet assembly. Asindicated earlier, an interior volume for cathode may need to besubstantially larger than the other active elements in the battery. Muchof a battery construct may have to create the space of this cathodematerial, and support it from migration during flexing of the battery.Another portion of the battery construct that may consume significantportions of the thickness budget may be the separator material. In someexamples, a sheet form of separator may create an advantageous solutionfor laminate processing. In other examples, the separator may be formedby dispensing hydrogel material into a layer to act as the separator.

In these laminate battery assembly examples, the forming product mayhave an anode sheet, which may be a combination of a package layer andan anode current collector, as well as substrate for the anode layer.The forming product may also have an optional separator spacer sheet, acathode spacer sheet, and a cathode sheet. The cathode sheet may be acombination of a package layer and a cathode current collector layer.

Intimate contact between electrodes and current collectors is ofcritical importance for reducing impedance and increasing dischargecapacity. If portions of the electrode are not in contact with thecurrent collector, resistance may increase since conductivity is thenthrough the electrode (typically less conductive than the currentcollector) or a portion of the electrode may become totallydisconnected. In coin cell and cylindrical batteries, intimacy isrealized with mechanical force to crimp the can, pack paste into a can,or through similar means. Wave washers or similar springs are used incommercial cells to maintain force within the battery; however, thesewould add to the overall thickness of a miniature battery. In typicalpatch batteries, a separator may be saturated in electrolyte, placedacross the electrodes, and pressed down by the external packaging. In alaminar, cofacial battery there are several methods to increaseelectrode intimacy. The anode may be plated directly onto the currentcollector rather than using a paste. This process inherently results ina high level of intimacy and conductivity. The cathode; however, istypically a paste. Although binder material present in the cathode pastemay provide adhesion and cohesion, mechanical pressure may be needed toensure the cathode paste remains in contact with the cathode currentcollector. This may be especially important as the package is flexed andthe battery ages and discharges, for example, as moisture leaves thepackage through thin and small seals. Compression of the cathode may beachieved in the laminar, cofacial battery by introducing a compliantseparator and/or electrolyte between the anode and cathode. A gelelectrolyte or hydrogel separator, for example, may compress on assemblyand not simply run out of the battery as a liquid electrolyte would.Once the battery is sealed, the electrolyte and/or separator may thenpush back against the cathode. An embossing step may be performed afterassembly of the laminar stack, introducing compression into the stack.

Exemplary Illustrated Processing of Biocompatible EnergizationElements—Placed Separator

An example of the steps that may be involved in processing biocompatibleenergization elements may be found referring to FIGS. 4A-4N. Theprocessing at some of the exemplary steps may be found in the individualfigures. In FIG. 4A, a combination of a PET Cathode Spacer 401 and a PETGap Spacer 404 may be illustrated. The PET Cathode Spacer 401 may beformed by applying films of PET 403 which, for example, may be roughly 3mils thick. On either side of the PET layer may be found PSA layers orthese may be capped with a polyvinylidene fluoride (PVDF) release layer402 which may be roughly 1 mil in thickness. The PET Gap spacer 404 maybe formed of a PVDF layer 409 which may be roughly 3 mils in thickness.There may be a capping PET layer 405 which may be roughly 0.5 mils inthickness. Between the PVDF layer 409 and the capping PET layer 405, insome examples, may be a layer of PSA.

Proceeding to FIG. 4B, a hole 406 in the Gap spacer layer may be cut bylaser cutting treatment. Next at FIG. 4C, the cut PET Gap spacer layermay be laminated 408 to the PET Cathode Spacer layer. Proceeding to FIG.4D, a cathode spacer hole 410 may be cut by laser cutting treatment. Thealignment of this cutting step may be registered to the previously cutfeatures in the PET Gap spacer Layer. At FIG. 4E, a layer of Celgard412, for an ultimate separator layer, may be bonded to a carrier 411.Proceeding to FIG. 4F, the Celgard material may be cut to figures thatare between the size of the previous two laser cut holes, andapproximately the size of the PET gap spacer hole, forming a precutseparator 420. Proceeding to FIG. 4G, a pick and place tool 421 may beused to pick and place discrete pieces of Celgard into their desiredlocations on the growing device. At FIG. 4H, the placed Celgard pieces422 are fastened into place and then the PVDF release layer 423 may beremoved. Proceeding to FIG. 4I, the growing device structure may bebonded to a film of the anode 425. The anode may be comprised of ananode collector film upon which a zinc anode film has beenelectrodeposited.

Proceeding to FIG. 4J, a cathode slurry 430 may be placed into theformed gap. A squeegee 431 may be used in some examples to spread thecathode mix across a work piece and in the process fill the gaps of thebattery devices being formed. After filling, the remaining PVDF releaselayer 432 may be removed which may result in the structure illustratedin FIG. 4K. At FIG. 4L the entire structure may be subjected to a dryingprocess which may shrink the cathode slurry 440 to also be at the heightof the PET layer top. Proceeding to FIG. 4M, a cathode film layer 450,which may already have the cathode collector film upon it, may be bondedto the growing structure. In a final illustration at FIG. 4N a lasercutting process may be performed to remove side regions 460 and yield abattery element 470. There may be numerous alterations, deletions,changes to materials and thickness targets that may be useful within theintent of the present disclosure.

The result of the exemplary processing may be depicted in some detail atFIG. 5. In an example, the following reference features may be defined.The Cathode chemistry 510 may be located in contact with the cathode andcathode collector 520. A pressure sensitive adhesive layer 530 may holdand seal the cathode collector 520 to a PET Spacer layer 540. On theother side of the PET Spacer layer 540, may be another PSA layer 550,which seals and adheres the PET Spacer layer 540 to the PET Gap layer560. Another PSA layer 565 may seal and adhere the PET Gap layer 560 tothe Anode and Anode Current Collector layers. A Zinc Plated layer 570may be plated onto the Anode Current Collector 580. The separator layer590 may be located within the structure to perform the associatedfunctions as have been defined in the present disclosure. In someexamples, an electrolyte may be added during the processing of thedevice, in other examples, the separator may already compriseelectrolyte.

Exemplary Processing Illustration of Biocompatible EnergizationElements—Deposited Separator

An example of the steps that may be involved in processing biocompatibleenergization elements may be found in FIGS. 6A-6F. The processing atsome of the exemplary steps may be found in the individual figures.There may be numerous alterations, deletions, changes to materials andthickness targets that may be useful within the intent of the presentdisclosure.

In FIG. 6A, a laminar construct 600 may be illustrated. The laminarstructure may comprise two laminar construct release layers 602 and 602a, one layer on either end; two laminar construct adhesive layers 604and 604 a, located between the laminar construct release layers 602 and602 a; and a laminar construct core 606, located between the two laminarconstruct adhesive layers 604 and 604 a. The laminar construct releaselayers 602 and 602 a and adhesive layers 604 and 604 a may be producedor purchased, such as a commercially available pressure sensitiveadhesive transfer tape with primary liner layer. The laminar constructadhesive layers 604 may be a PVDF layer which may be approximately 1-3millimeters in thickness and cap the laminar construct core 606. Thelaminar construct core 606 may comprise a thermoplastic polymer resinsuch as polyethylene terephthalate (PET), which for example, may beroughly 3 millimeters thick. Proceeding to FIG. 6B, a hole for thecathode pocket 608 may be cut in the laminar construct by laser cuttingtreatment. This may form a cathode spacer layer.

Next, at FIG. 6C, the bottom laminar construct release layer 602 may beremoved from the laminar construct, exposing the laminar constructadhesive layer 604. The laminar construct adhesive layer 604 may then beused to adhere an anode connection foil 610 to cover the bottom openingof the cathode pocket 608. Proceeding to FIG. 6D, the anode connectionfoil 610 may be protected on the exposed bottom layer by adhering amasking layer 612. The masking layer 612 may be a commercially availablePSA transfer tape with a primary liner. Next, at FIG. 6E, the anodeconnection foil 610 may be electroplated with a coherent metal 614, Zincfor example, which coats the exposed section of the anode connectionfoil 610 inside of the cathode pocket. Proceeding to 6F, the anodeelectrical collection masking layer 612 is removed from the bottom ofthe anode connection foil 610 after electroplating. In some examples, tobe discussed in a later section, materials may be coated into the cavityother than metals, such as deposits of graphite, graphite intercalatedwith metals or semiconductor layers.

FIGS. 7A-7F may illustrate an alternate mode of processing the methodsteps illustrated in FIGS. 6A-6F. FIGS. 7A-7B may illustrate similarprocesses as depicted in FIGS. 6A-6B. The laminar structure may comprisetwo laminar construct release layers, 702 and 702 a, one layer on eitherend; two laminar construct adhesive layers, 704 and 704 a, locatedbetween the laminar construct release layers 702 and 702 a; and alaminar construct core 706, located between the two laminar constructadhesive layers 704 and 704 a. The laminar construct release layers andadhesive layers may be produced or purchased, such as a commerciallyavailable pressure-sensitive adhesive transfer tape with primary linerlayer. The laminar construct adhesive layers may be a polyvinylidenefluoride (PVDF) layer which may be approximately 1-3 millimeters inthickness and cap the laminar construct core 706. The laminar constructcore 706 may comprise a thermoplastic polymer resin such as polyethyleneterephthalate, which for example may be roughly 3 millimeters thick.Proceeding to FIG. 7B, a cavity for the cathode pocket 708 may be cut inthe laminar construct by laser cutting treatment. In FIG. 7C, an anodeconnection foil 710 may be obtained and a protective masking layer 712applied to one side. Next, at FIG. 7D, the anode connection foil 710 maybe electroplated with a layer 714 of a coherent metal, for example,zinc. Proceeding to FIG. 7E, the laminar constructs of FIGS. 7B and 7Dmay be combined to form a new laminar construct as depicted in FIG. 7Eby adhering FIG. 7B to the electroplated layer 714 of FIG. 7D. Therelease layer 702 a of FIG. 7B may be removed in order to exposeadhesive layer 704 a of FIG. 7B for adherence onto electroplated layer714 of FIG. 7D. Proceeding next to FIG. 7F, the anode protective maskinglayer 712 may be removed from the bottom of the anode connection foil710.

FIGS. 8A-8H may illustrate implementation of energization elements to abiocompatible laminar structure, which at times is referred to as alaminar assembly or a laminate assembly herein, similar to, for example,those illustrated in FIGS. 6A-6F and 7A-7F. Proceeding to FIG. 8A, ahydrogel separator precursor mixture 820 may be deposited on the surfaceof the laminate assembly. In some examples, as depicted, the hydrogelprecursor mixture 820 may be applied upon a release layer 802. Next, atFIG. 8B, the hydrogel separator precursor mixture 820 may be squeegeed850 into the cathode pocket while being cleaned off of the release layer802. The term “squeegeed” may generally refer to the use of aplanarizing or scraping tool to rub across the surface and move fluidmaterial over the surface and into cavities as they exist. The processof squeegeeing may be performed by equipment similar to the vernacular“Squeegee” type device or alternatively and planarizing device such asknife edges, razor edges and the like which may be made of numerousmaterials as may be chemically consistent with the material to be moved.

The processing depicted at FIG. 8B may be performed several times toensure coating of the cathode pocket, and increment the thickness ofresulting features. Next, at FIG. 8C, the hydrogel separator precursormixture may be allowed to dry in order to evaporate materials, which maytypically be solvents or diluents of various types, from the hydrogelseparator precursor mixture; then, the dispensed and applied materialsmay be cured. It may be possible to repeat both of the processesdepicted at FIG. 8B and FIG. 8C in combination in some examples. In someexamples, the hydrogel separator precursor mixture may be cured byexposure to heat while in other examples the curing may be performed byexposure to photon energy. In still further examples the curing mayinvolve both exposure to photon energy and to heat. There may benumerous manners to cure the hydrogel separator precursor mixture.

The result of curing may be to form the hydrogel separator precursormaterial to the wall of the cathode pocket as well as the surface regionin proximity to an anode or cathode feature which in the present examplemay be an anode feature. Adherence of the material to the sidewalls ofthe cavity may be useful in the separation function of a separator. Theresult of curing may be to form a dehydrated polymerized precursormixture concentrate 822 which may be simply considered the separator ofthe cell. Proceeding to FIG. 8D, cathode slurry 830 may be depositedonto the surface of the laminar construct release layer 802. Next, atFIG. 8E the cathode slurry 830 may be squeegeed into the cathode pocketand onto the dehydrated polymerized precursor mixture concentrate 822.The cathode slurry may be moved to its desired location in the cavitywhile simultaneously being cleaned off to a large degree from thelaminar construct release layer 802. The process of FIG. 8E may beperformed several times to ensure coating of the cathode slurry 830 ontop of the dehydrated polymerized precursor mixture concentrate 822.Next, at FIG. 8F, the cathode slurry may be allowed to dry down to forman isolated cathode fill 832 on top of the dehydrated polymerizedprecursor mixture concentrate 822, filling in the remainder of thecathode pocket.

Proceeding to FIG. 8G, an electrolyte formulation 840 may be added on tothe isolated cathode fill 832 and allowed to hydrate the isolatedcathode fill 832 and the dehydrated polymerized precursor mixtureconcentrate 822. Next, at FIG. 8H, a cathode connection foil 816 may beadhered to the remaining laminar construct adhesive layer 804 byremoving the remaining laminar construct release layer 802 and pressingthe connection foil 816 in place. The resulting placement may result incovering the hydrated cathode fill 842 as well as establishingelectrical contact to the cathode fill 842 as a cathode currentcollector and connection means.

FIGS. 9A through 9C may illustrate an alternative example of theresulting laminate assembly illustrated in FIG. 7D. In FIG. 9A, theanode connection foil 710 may be obtained and a protective masking layer712 applied to one side. The anode connection foil 710 may be platedwith a layer 714 of coherent metal with, for example, zinc in a similarfashion as described in the previous figures. Proceeding to FIG. 9B, ahydrogel separator 910 may be applied without the use of the squeegeemethod illustrated in FIG. 8E. The hydrogel separator precursor mixturemay be applied in various manners, for example, a preformed film of themixture may be adhered by physical adherence, and alternatively adiluted mixture of the hydrogel separator precursor mixture may bedispensed and then adjusted to a desired thickness by the processing ofspin coating. Alternatively the material may be applied by spraycoating, or any other processing equivalent.

Next, at FIG. 9C, processing is depicted to create a segment of thehydrogel separator that may function as a containment around a separatorregion. The processing may create a region that limits the flow, ordiffusion, of materials such as electrolyte outside the internalstructure of the formed battery elements. Such a blocking feature 920 ofvarious types may therefore be formed. The blocking feature, in someexamples, may correspond to a highly crosslinked region of the separatorlayer as may be formed in some examples by increased exposure to photonenergy in the desired region of the blocking feature 920. In otherexamples, materials may be added to the hydrogel separator materialbefore it is cured to create regionally differentiated portions thatupon curing become the blocking feature 920. In still further examples,regions of the hydrogel separator material may be removed either beforeor after curing by various techniques including for example chemicaletch of the layer with masking to define the regional extent. The regionof removed material may create a blocking feature in its own right oralternatively materially may be added back into the void to create ablocking feature. The processing of the impermeable segment may occurthrough several methods including but not limited to: image outprocessing, increased cross-linking, heavy photodosing, back-filling, oromission of hydrogel adherence to create a void. In some examples, alaminate construct or assembly of the type depicted as the result of theprocessing in FIG. 9C may be formed without the blocking feature 920.

Polymerized Battery Element Separators

In some battery designs, the use of a discrete separator (as describedin a previous section) may be precluded due to a variety of reasons suchas the cost, the availability of materials, the quality of materials, orthe complexity of processing for some material options as non-limitingexamples. In such cases, a cast or form-in-place separator which mayhave been depicted in the processes of FIGS. 8A-8H for example, mayprovide desirable benefits. While starch or pasted separators have beenused commercially with success in AA and other format Leclanche or zinccarbon batteries, such separators may be unsuitable in some ways for usein certain examples of laminar microbatteries. Particular attention mayneed to be paid to the uniformity and consistency of geometry for anyseparator used in the batteries of the present disclosure. Precisecontrol over separator volume may be needed to facilitate precisesubsequent incorporation of known cathode volumes and subsequentrealization of consistent discharge capacities and cell performance.

A method to achieve a uniform, mechanically robust form-in-placeseparator may be to use UV-curable hydrogel formulations. Numerouswater-permeable hydrogel formulations may be known in variousindustries, for example, the contact lens industry. An example of acommon hydrogel in the contact lens industry may be poly(hydroxyethylmethacrylate) crosslinked gel, or simply pHEMA. Fornumerous applications of the present disclosure, pHEMA may possess manyattractive properties for use in Leclanche and zinc carbon batteries.pHEMA typically may maintain a water content of approximately 30-40percent in the hydrated state while maintaining an elastic modulus ofabout 100 psi or greater. Furthermore, the modulus and water contentproperties of crosslinked hydrogels may be adjusted by one of skill inthe art by incorporating additional hydrophilic monomeric (e.g.methacrylic acid) or polymeric (e.g. polyvinylpyrrolidone) components.In this manner, the water content, or more specifically, the ionicpermeability of the hydrogel may be adjusted by formulation.

Of particular advantage in some examples, a castable and polymerizablehydrogel formulation may contain one or more diluents to facilitateprocessing. The diluent may be chosen to be volatile such that thecastable mixture may be squeegeed into a cavity, and then allowed asufficient drying time to remove the volatile solvent component. Afterdrying, a bulk photopolymerization may be initiated by exposure toactinic radiation of appropriate wavelength, such as blue UV light at420 nm, for the chosen photoinitiator, such as CG 819. The volatilediluent may help to provide a desirable application viscosity so as tofacilitate casting a uniform layer of polymerizable material in thecavity. The volatile diluent may also provide beneficial surface tensionlowering effects, particularly in the case where strongly polar monomersare incorporated in the formulation. Another aspect that may beimportant to achieve the casting of a uniform layer of polymerizablematerial in the cavity may be the application viscosity. Common smallmolar mass reactive monomers typically do not have very highviscosities, which may be typically only a few centipoise. In an effortto provide beneficial viscosity control of the castable andpolymerizable separator material, a high molar mass polymeric componentknown to be compatible with the polymerizable material may be selectedfor incorporation into the formulation. Examples of high molar masspolymers which may be suitable for incorporation into exemplaryformulations may include polyvinylpyrrolidone and polyethylene oxide.

In some examples the castable, polymerizable separator may beadvantageously applied into a designed cavity, as previously described.In alternative examples, there may be no cavity at the time ofpolymerization. Instead, the castable, polymerizable separatorformulation may be coated onto an electrode-containing substrate, forexample, patterned zinc plated brass, and then subsequently exposed toactinic radiation using a photomask to selectively polymerize theseparator material in targeted areas. Unreacted separator material maythen be removed by exposure to appropriate rinsing solvents. In theseexamples, the separator material may be designated as aphoto-patternable separator.

Primary Battery Example

In some examples of the processing of biocompatible energizationelements with deposited separators, a primary battery may be formed. Atypical primary battery may be characterized by its single-use property.In an example consistent with the laminar processing, a battery may beformed with the following characteristics and elements as set forth inthe Table below.

Element Material Cathode Current Collector Titanium Foil CathodeElectrode (Slurry) Slurry Containing Electrolytic Manganese Dioxide andCarbon Separator Hydrogel Anode Electrode Electrodeposited Zinc AnodeCurrent Collector Brass Foil Laminate Polyethylene Terphalate Core withAdhesive Electrolyte ZnCl₂/NH₄Cl Base

There may be numerous formulations of cathode chemistry that may beconsistent with this invention. As a non-limiting example, a formulationmay comprise electrolytic manganese dioxide in a graphite mixture. Inone example, a powder mixture may be formed by mixing jet-milledelectrolytic manganese dioxide (JMEMD) and KS6 graphite as availablefrom Timcal (TIMCAL TIMREX® KS6 Primary Synthetic Graphite) in a 80percent JMEMD to 20 percent KS6 ratio by weight. The mixing may beperformed by numerous means. For example, the JMEMD and KS6 may be mixedby grind milling the two powders for an extended period on the order ofminutes to hours. In some examples, the resulting powder mixture may bemixed with a 10 percent polyisobutylene (PIB) in toluene solution. The10 percent PIB solution may be formed from polyisobutylene grade B50mixed with toluene in a roughly 10 parts PIB B50 to 90 parts tolueneformulation by weight. The 10 percent PIB may be mixed with anadditional amount of toluene and with the JMEMD/K6 powder to formulate aslurry for cathode processing. This mixture of these materials may startwith approximately 1.5 parts PIB B50/Toluene solution. To this,approximately 2.3 parts Toluene may be added. The mixture may becompleted with 4.9 parts JMEMD/KS6 powder. This may result in a mixturethat is approximately 1.7 percent PIB, 45 percent JMEMD, 11 percent KS6,and the remainder, toluene. The mixing may proceed until a uniformslurry with a paste-like consistency is formed. The amount of solvent(toluene in an example) in the system may be varied to affect thecharacteristics of the slurry formed, and in other examples, therelative amount of PIB B50 in the slurry may be varied from the example.

Continuing with the primary battery example, a hydrogel separator may beformed in the manners discussed in this disclosure from a precursormixture. In one example, a precursor mixture may be formed by mixinghydroxyethylmethacrylate (HEMA) with ethylene glycol dimethylacrylate(EGDMA) and with polyvinylpyrrolidone (PVP). There may be otherconstituents added to the mixture such as photoinitiators. An exemplaryphotoinitiator may be phenylbis (2,4,6-trimethylbenzoyl)-phosphineoxide, which may be available in commercial formulations includingIrgacure® 819, which may also be called “CGI 819” herein. There may alsobe numerous solvents that may be used in varying amounts to reach adesired rheology of the mixture. In a non-limiting example, 2-proponolmay be used as an appropriate solvent.

Many of the general discussions on elements of biocompatibleenergization devices, such as the cathode and cathode slurry, haveexamples related to primary battery elements, and the variations andexamples for these various elements may be expected to comprise otherexamples of primary battery elements for the present specification.

In some examples, the zinc anode may be formed by electrodepositing thezinc upon the anode current collector material. In other examples, ashave been discussed, the electrodeposition may occur through thelaminate structure to only exposed portions of the anode currentcollector material. There may be numerous manners of depositing anodematerials, for example, lamination or metal cladding; and, other batterysystems may employ other chemical species other than zinc, such assilver as a non-limiting example.

The battery may include various types of electrolyte formulations. Basicsolutions of hydroxide may be included in the electrolyte. However, insome examples of biocompatible batteries, less basic electrolyteformulations may be utilized. Electrolytes for use in the presentinvention may include zinc chloride, zinc acetate, ammonium acetate,ammonium chloride, and similar salts in mass concentrations fromapproximately 0.1 percent to 30 percent. In addition, surfactants may beadded to the electrolyte formulation, for example to improve wetting orreduce corrosion. Exemplary surfactants may include Triton™ X-100,Triton™ QS44, and Dowfax™ 3B2 in concentrations from 0.01 percent to 2percent. As an example Triton™ X-100 may be added to the zinc chloride,ammonium chloride solution. One example of an electrolyte formulationmay be: 20% zinc chloride, 500 ppm of Triton® QS-44, 200 ppm of indium+3 ion supplied as indium acetate, and balance with water.

Secondary Battery Examples

The structure and manufacturing processes that have been described inthe present disclosure may be useful in general for the production ofsecondary, or rechargeable, batteries. There may be a number ofconsiderations related to secondary battery elements that may differfrom considerations made for primary elements. The recharging processfor a battery element may result in swelling and shrinking of batterycomponents, and therefore the dimensions of features and containmentlayers as well as the composition of the battery may be adjusted in someembodiments. The use of gelled polymer layers for the electrolytes mayallow for a layer which may take up some of the swelling and shrinkingaspects as electrode ions are moved around the device during chargingcycles, and subsequently, during discharging cycles.

In secondary batteries, the anode and cathode layers may switchdesignation depending on whether the device is charging or discharging,and may be considered first and second electrodes. Therefore, it may beuseful to refer to the anode and cathode in reference to whether thebattery cell is being charged, such that it may be considered anelectrolytic cell, or whether it is being discharged, such that it maybe considered a galvanic cell. Therefore, when referred to as thecathode of the galvanic cell, the first electrode structure wouldfunction to spontaneously accept electrons from an externally connectedcircuit. Conversely, the cathode of the electrolytic cell would functionto accept electrons from an external charging element.

Although in some examples the zinc manganese dioxide class of batteriesmay function as a secondary battery, there are many more common examplesof secondary batteries. In a common class of secondary batteries,lithium ions may comprise the energy storing chemical species. There maybe numerous manners to form electrodes in lithium ion batteries. In thetype of devices according to the present invention, there may benumerous intercalated lithium compounds that might be present in theanode of the galvanic cell. For example, the cathode slurry may includeLithium Nickel Manganese Cobalt Oxide, Lithium Manganese Oxide, andLithium Iron Phosphate amongst others.

The second electrode may be the anode of the galvanic cell. In someexamples, the second electrode may be formed of, or coated with,graphite or other forms of carbon. In other examples, various forms ofdeposited silicon may be used. In similar manners to the electroplatingof zinc discussed with respect to primary batteries, silicon may beelectroplated either in regions or in a flat layer across the substrate.Electroplated silicon may be formed onto the electrode metal contactlayer, which may have surface coatings of platinum, titanium or a thinlayer of silicon in some examples. The platting of the electrodematerial may occur in non-aqueous media comprising SiCl₄, SiHCL₃, SiBr₄,Si(Ch₂Ch₃)₄, or Si(OOCCH₃)₄ as non-limiting examples. In other examples,graphite or silicon layers may be sputter deposited to the currentcollector surface to form the second current collector region in amanner similar to that depicted at FIG. 7D.

The electrodes may be formed upon metal sheets in manners consistentwith the prior discussions relating to laminate processing. Theseelectrodes and metal sheets may form the base layer: i.e. underneath thelaminate layers that form the cavity. Also, the other current collectormay be used to cap the laminate structure after the cathode has beenformed and the cell has been filled with electrolyte.

To form electrolyte solutions, lithium salts may typically be dissolvedin non-aqueous solvent systems. Therefore, these non-aqueous solventsystems may interact with the various adhesive layers in differentmanners, and since the integrity of seals in the battery devices may beimportant, there may be alterations in the choice of adhesive systemsthat may be required depending on the use of non-aqueous solvents.Gelled forms of polymer electrolytes are known in lithium polymerdevices incorporating polymer electrolytes. The methods of formation ofseparators starting with liquid precursor filling of a cavity may beperformed for these types of secondary batteries where a polymerizedseparator may be formed from polymers such as PVDF orpoly(acrylonitrile). In some examples, it may be possible to utilizehydrogel forming precursors where the polymer is gelled withconventional salts consistent with Lithium cells. For example, in anon-limiting example, a separator precursor may be mixed with lithiumhexafluorophosphate in non-aqueous solvents such as ethylene carbonate,dimethyl carbonate, and diethyl carbonate as non-limiting examples. Theresulting gelled layer may be formed with excess solvent to allow forshrinkage as has been described in relationship to the hydrogelprecursor processing.

In a specific non-limiting example, a cavity-based laminate structuremay be formed (as has been described in the prior discussion of laminateprocessing) where the bottom layer may be the current collector uponwhich a graphite or silicon layer has been attached. The laminate layersthat attach to the current collector may have the cavities formed intothem as has been described. In a non-limiting example, a castingsolution may be formed by mixing a roughly two to one ratio ofpoly(vinylidene fluoride) (PVDF) and poly(dimethylsiloxane) (PDMS),respectively, into a solvent mixture comprising N—N Dimethyl Acetamide(DMAc) and glycerol. The ratio of the DMAc to glycerol may be varied andmay affect characteristics such as the porosity of the resultingseparator layer. An excess of the solvent mixture may be used to allowfor the shrinkage of the resulting layer in the cavity to form a thinseparator layer. In some examples, especially for high levels ofsolvent, the adhesive system for the laminate structure may be alteredto optimize consistency with the DMAc-glycerol solvent system. Aftersqueegee processing of the casting solution into the defined cavities,the resulting structure may be dried at room temperature or elevatedtemperature for some time period. Other manners of dispensing thecasting solution may be consistent with the processes described herein.Thereafter, the structure may be immersed into a room temperature waterbath for 20-40 hours to allow for the glycerol to dissolve out of theseparator layer and result in a layer with a desired porosity. Theresulting structure may then be dried in a vacuum environment over aperiod of 20-40 hours.

In some examples, the resulting separator layer may be treated withexposure to an electrolyte solution. In a non-limiting example a 1 MolarLithium Hexafluorophosphate solution in a roughly 1/1/1 mixture ofEthylene Carbonate (EC)/Dimethyl Carbonate (DMC) and Ethyl MethylCarbonate (EMC) may be formed and dispensed into the cavity. In someother examples exposure to the electrolyte may occur after the cathodeis formed into the cavity.

In a different type of example the laminate structure may be built inthe manner outlined in reference to FIGS. 4A-4N. A separator, such as afilm of Celgard, may be cut to a size of a feature in a gap spacer layerand then placed into the laminate structure as opposed to being filedinto the cavity. The placed separator may also be treated with anexposure to electrolyte before further processing with a “cathodeslurry.”

The resulting structure may now be ready to receive a treatment with thecathode slurry. A number of cathode slurries comprising different typesof lithium compounds may be used; although, other chemical types thanlithium may be possible. In a non-limiting example, a lithium ironphosphate (LiFePO4) based slurry may be used. In some examples thelithium iron phosphate slurry may be formed by first mixing sodiumcarboxymethyl cellulose in deionized water. To the resulting mixture, apowder comprising Lithium Iron Phosphate and conductive agents such assynthetic graphite and carbon black may then be added and extensivelymixed. Next, a further refined slurry may be formed by adding styrenebutadiene rubber and extensively mixing. The slurry may then beprocessed into the cavity structure in means as have been described inthe present disclosure such as through use of a squeegee process. Therheology of the slurry may be adjusted for optimizing the integrity ofthe squeegee based filing process, for example, by adding or removingsolvent or by adjusting the relative amount of the styrene butadienerubber added. The resulting filled structure may then be dried in avacuum environment over 20-40 hours.

In some examples, the resulting cathode and separator layers may betreated with exposure to an electrolyte solution. In a non-limitingexample a 1 Molar Lithium Hexafluorophosphate solution in a roughly1/1/1 mixture of Ethylene Carbonate (EC)/Dimethyl Carbonate (DMC) andEthyl Methyl Carbonate (EMC) may be formed and dispensed into thecavity. In some examples, the electrolyte may be added to the cathodewith the assistance of either pressure treatment or vacuum treatment toenhance the diffusion of the electrolyte mixture into the layers.

The second current collector layer may be attached to the laminatestructure after the removal of a release layer from laminate structure.The adhered electrode may contact the deposited slurry and provideelectrical contact between the metal current collector and theelectrolyte infused cathode resulting in a battery structure.

The biocompatible devices may be, for example, implantable electronicdevices, such as pacemakers and micro-energy harvesters, electronicpills for monitoring and/or testing a biological function, surgicaldevices with active components, ophthalmic devices, microsized pumps,defibrillators, stents, and the like.

Specific examples have been described to illustrate embodiments for theformation, methods of formation, and apparatus of formation ofbiocompatible energization elements comprising separators. Theseexamples are for said illustration and are not intended to limit thescope of the claims in any manner. Accordingly, the description isintended to embrace all embodiments that may be apparent to thoseskilled in the art.

What is claimed is:
 1. A biocompatible energization element comprising agap spacer layer; a first hole located in the gap spacer layer; acathode spacer layer, wherein the cathode spacer layer is attached tothe gap spacer layer; a second hole located in the cathode spacer layer,wherein the second hole is aligned to the first hole, and wherein thesecond hole is smaller than the first hole such that when the first holeand the second hole are aligned there is a ridge of cathode spacer layerexposed in the first hole; a separator layer, wherein the separatorlayer is placed within the first hole in the gap spacer layer and isadhered to the ridge of cathode spacer layer; a cavity between sides ofthe second hole and a first surface of the separator layer, wherein thecavity is filled with cathode chemicals; a first current collectorcoated with anode chemicals; a second current collector, wherein thesecond current collector is in electrical connection with the cathodechemicals; and an electrolyte comprising electrolyte chemicals, whereinthe cathode chemicals, anode chemicals and electrolyte chemicals areformulated for a single discharging cycle of the energization element.2. The biocompatible energization element of claim 1 wherein the cathodechemicals comprise a salt of manganese.
 3. The biocompatibleenergization element of claim 2 wherein the cathode chemicals comprisemanganese dioxide.
 4. The biocompatible energization element of claim 1wherein the anode chemicals comprise zinc.
 5. The biocompatibleenergization element of claim 4 wherein the anode chemicals compriseelectrodeposited zinc.
 6. The biocompatible energization element ofclaim 1 wherein the cathode chemicals comprise graphite.
 7. Thebiocompatible energization element of claim 1 wherein the cathodechemicals comprise polyisobutylene.
 8. The biocompatible energizationelement of claim 1 wherein the cathode chemicals comprise toluene. 9.The biocompatible energization element of claim 1 wherein the cathodechemicals comprise jet milled electrolytic manganese dioxide.
 10. Thebiocompatible energization element of claim 1 wherein the cathodechemicals comprise KS6 primary synthetic graphite.
 11. The biocompatibleenergization element of claim 10 wherein the cathode chemicals comprisea mixture of approximately 1.7 percent PIB B50, 45 percent JMEMD, 11percent KS6, and the remainder, Toluene.
 12. The biocompatibleenergization element of claim 1 wherein the electrolyte comprises one ormore of zinc chloride and ammonium chloride.
 13. The biocompatibleenergization element of claim 1 wherein the separator comprises Celgard™412.
 14. The biocompatible energization element of claim 1 wherein thebiocompatible energization element is electrically connected to anelectroactive element within a biomedical device.
 15. The biocompatibleenergization element of claim 1 wherein the biocompatible energizationelement is electrically connected to an electroactive element within abiomedical device.
 16. The biocompatible energization element of claim15 wherein the biomedical device is an ophthalmic device.
 17. Thebiocompatible energization element of claim 16 wherein the ophthalmicdevice is a contact lens.